I just bought trackmania 2 stadium on steam and the game installed fine and everything. I was under the impression that this game would have a campaign or some sort of tutorial to get new players eased into the game. When I select to play in single player, the game leads me to a folder labelled 'Campaigns' but this folder just leads to five empty ones. I can play online with other players, but I tend to find some of the maps can be quite difficult, and there's a time limit for each one. Can anyone point me in the right direction? Do I need to find the campaign maps on this website?

Firstly, welcome to TrackMania! It's always nice to see new faces.

Secondly, each TM game comes with its own campaign (though there is no traditional tutorial, the controls are very easy to learn). To access it, first enter the title (in your case, Stadium). You should see four major options. Select the top option, which should be labeled "Solo" or your language's equivalent. From there, you can play the main campaign, which is divided into 5 difficulties from easy (white) to hard (black).

Alternatively, you could play player made stages. ManiaExchange is primarily for sharing custom maps, so feel free to browse and play the maps available here. Many courses players make are even better than the main campaign maps! Here's a track search for beginner Stadium courses which have recently had activity (be it just uploaded/updated or recently got a comment, award, or time):

https://tm.mania-exchange.com/tracksearch2?tpack=TMStadium&unreleased=0&priord=12&secord=6&envmix=0

As a rule of thumb, maps with a large number of awards are more likely to be good maps. Do remember that a lack of awards does not mean a course is bad, though!

If you have any further questions, don't hesitate to ask!