From TM Wiki

Mods are almost little more than just different textures for all Trackmanias. Some of these include "ports" (that is, conversions) of textures from one environment to another, but most are largely original.

Where to find mods

Mod-makers can usually find mentioning of their mods at TM-Mod (link loads the EN version), but first they need to upload it to a file host, like YourFileLink. Some, though, prefer just to use these file hosters for people to download their mods.

There is a list of mods for (every?) Trackmania, see:

• TMO: TM-MOD Mod List (Original)
• TMS: MOD IDEAS - MOD WIP - FINISHED MODS - TMSX, TM-MOD Mod List (Sunrise)
• TMN: Mods list: WIP and completed, TM-MOD Mod List (Nations)

To Install mods

Save the .zip file (Do NOT unzip it) to: Gamedata/Skins/(environment)/Mod (If this folder doesn't exist, create it.)

To Use mods

Whilst in the game, make a new track. After selecting stats for your track (these "stats" only apply to TMO/S) you can choose the mod that your track will use. NOTE: Other players must have the mod to see the texture changes. It is not required to play the track.

To do ...