East Midlands Trains operate all trains from Matlock, and London trains from Nottingham, Derby, Chesterfield, and Sheffield. Their "walk-up" fares are horrendously expensive, but if you can plan ahead, there are some less-expensive deals to be had - as with other companies, the sooner you book, the less you pay. If you can be flexible about when you travel, you can travel for as little as £13 each way between Sheffield, Chesterfield, or Derby and London, with a Megatrain deal. As you'd expect, availability is limited to the least popular trains, but if you can get organised enough to book ahead - and work within their restrictions, this can be a good deal.
If you are travelling a reasonable distance, it can be usefully cheaper to split your journey into sections and buy separate tickets for each section: the rule is that your train must stop at the station where your tickets join (but you don't need to get off). For example, Matlock-Leamington costs £42-odd for the cheapest (off-peak) return: you can cut this to under £30 by buying returns for Matlock-Burton and Burton-Leamington. The Trainsplit website will suggest splits, in return for 10% of the saving.
If your trip includes travel on the East Coast Main Line (London-Peterborough-Doncaster-York-Newcastle-Edinburgh-Glasgow) it can be usefully cheaper to buy a fixed-train ticket for the East Coast section separately using the East Coast website. If your trip involves using a Cross-Country service (Plymouth or Cardiff-Bristol-Birmingham-Chesterfield-Sheffield-York-Newcastle-Edinburgh), then using their website allows you to choose exactly which seats are reserved for you (at least on Cross-Country services) - but they apparently make additional charges for posting tickets AND for collecting tickets from a machine.
Otherwise, try RedSpottedHanky - a very user-friendly site (with a really good Best Fare Finder) and no extra charges for collecting tickets from a ticket machine or for normal postage. Be aware that Matlock may not appear on the list of stations from which you can opt to collect your ticket - but actually it doesn't matter; you can nominate any ticket machine (eg Derby, which is on their list) and they have confirmed that you can collect your ticket from any other machine (eg Matlock). To their shame, they advertise a £1-a-minute phone number for resolving problems, but I have read suggestions that 01902 627981 or even 0800 3777748 will get you through to the same place. East Midlands Trains' own website also sells tickets without extra charges, but it isn't as user-friendly.
The Trainline are probably the best-known booking system but they add extra charges even for collecting a ticket from a machine, so best avoided.
Winster's nearest railway station is at Matlock, at the end of a single-track branch-line with trains every hour (two-hourly on Sundays) to Derby and Nottingham. Click Here for current "departure board" information for Matlock - it doesn't pick up delays once trains have left Ambergate, but it can still be useful.
There is a ticket machine at Matlock station. This will sell you tickets for immediate travel, and you can also use it to collect tickets that you have bought online. (Although the online systems ask you to specify which station you will collect from, it appears that whichever station you nominate, you can take your reference number and credit card to any ticket machine and it will retrieve and print out your booking.) According to the rules, if you get on a train at Matlock without a ticket, you might only be offered a full-price fully-flexible ticket - but at the moment, guards seem to be more flexible.
Connections at Derby for trains to London are pretty good.
Only those of a sporting disposition should think of combining train and bus to get to Winster via Matlock: whilst there are a few times in the day when a train arrival at Matlock appears to fit well with a bus departure from outside (eg at 1828), the timings are too tight to make for a reliable connection: bus drivers have no idea of (nor particular concern for) whether the train has arrived or not. When the connection works it is great, but you need a Plan B in case the train is more than a couple of minutes late.
Watch out for Sunday (and sometimes Saturday) engineering works - the less-than-intelligent people at East Midlands Trains time the replacement bus to take over an hour from Derby, and the bus arrives enormously early at each stop, then waits for ages until the allotted departure time. Towards Derby, the replacement bus leaves much earlier than the train it replaces - if travelling at a weekend, do check first - 08457 484950, or see below for online options.
Parking at Matlock station costs £4.50 per day; at Cromford or Whatstandwell it is £2.50 per day.
The nearest mainline station is at Chesterfield - the far side of town, but not too bad to reach even at busy times. The station car park has CCTV (albeit just a couple of cameras) and charges £11 per 24 hours if you arrive before 10am on a weekday, otherwise £5.50 per 24 hours. There's a much cheaper car park off the roundabout just before the station (but be very careful to park in marked bays - they are hot on penalties). There is also onstreet parking for free in Piccadilly Road which seems reasonably safe and is within about five minutes' walk (a bit spooky really late at night, but OK otherwise). Unfortunately, many types of ticket to London from Chesterfield are considerably more expensive than from Derby or Matlock.
Derby has nearly all of Chesterfield's trains (and the odd extra one too) but traffic problems are much more severe and the station is at the opposite side of the city centre. All three of their Car Parks are expensive - £14.50 per 24 hours for the more convenient car parks (and £11.50 at the other) - £7.50 for the first 24 hours if you arrive after 10am on a weekday or at weekends. When last checked, it seemed no cheaper to use City Centre car parks either (those with CCTV were even more expensive than the station).
For ease of access, it might be worth trying Long Eaton station (close to Junction 25 on the M1) where many Derby to London trains stop. For the greatest flexibility of service, Loughborough is an option - most trains on both the Derby and Nottingham lines stop there - but the car park only takes 140 cars, so may be an issue on busy days.
East Midlands Parkway station near Junction 24 of the M1, is potentially a better option for parking, but the timetable is not clever - it may boast two trains per hour, but these are very badly timed, with a 53-minute gap between trains if you are unlucky. The parking charge is currently (Sep 2018) £8 per day or £5.50 off-peak (from 0930).
Train travel to Leeds is easy, with a decent hourly service from Chesterfield - typically taking 1hr to 1hr30. Changing at Doncaster rather than Sheffield can result in a more comfortable journey.
For travel to Newcastle and Edinburgh, it is often easiest to drive to Doncaster (when I last checked: £10.50 per day weekday parking; £5/day at weekends). Newark is also a viable option - about 80 minutes' drive, but a secure car park (space may be tight on weekdays) and very fast trains from there to London or the North on the East Coast route.
For travel to Glasgow, Crewe (about 80 minutes by car) is often the best choice - but station car parking can fill up quite early in the day. Try online parking-space services for alternatives.
For Manchester, the line starts at Buxton (cheap parking if you buy a train ticket), but the service (mostly twice an hour, taking an hour) is very slow - you can usually overtake the train if you drive on to Disley (where the station is next to the A6). A bit further still is Hazel Grove station, which has more trains, and free parking (which fills up early in the day on weekdays). There is also the advantage that the 192 bus runs from Piccadilly Gardens to Hazel Grove every 10 minutes until the small hours (0040 Mon-Wed night, 0140 Thur night and 0255 on Fri and Sat nights when I last checked), so if you miss the last train (which is around 2310) you can still get home. A "Greater Manchester Wayfarer" ticket could be better value than ordinary tickets - ask at the station. For two people, check out "Duo" tickets. New Mills is another option (two stations on different lines, with New Mills Central having a slightly later last-train back from Manchester (dep 2324 last time I checked) - but I can't advise on parking options.
For "cheap" (Advance) tickets to the North-West (and, I suspect, Scotland via the West Coast line), there are sometimes much better options from Disley (and other stations between there and Stockport) than there are from Buxton (and stations to Furness Vale) - allowing you still to travel on the same train from Buxton, but saving a lot by combining a Buxton-Disley ticket with a Disley-onwards ticket.
Grindleford or Hathersage are also options for trains to Manchester (Hathersage is better if you want the first off-peak train in a morning) but beware that there is a chance that your train will be a noisy and rattly bus-body-on-rails "Pacer" unit. Note that there is the occasional two-hour gap between trains. Chinley has the occasional extra train, which goes through Manchester and on to Liverpool without a change.
There are many versions of the UK rail map online. The simples is the National Rail map - but it is only shows major stations in many areas. The most comprehensive is the Project Mapping version, but it is a bit clunky to navigate.
You can now consult a PDF file of the full National Rail Timetable online - but ridiculously, they publish corrections updates as a separate supplement rather than bothering to correct the original. So by all means browse the PDF files, but before relying on what you see, check with an online source to see if things have changed.
You can get train times from the National Rail Journey Planner - not perfect, but it includes some useful features, like the ability to find first and last trains of the day for any route. Alternatively, Google Maps allows you to plan public transport journeys including rail (choose Directions and then the "bus" logo)