How do I install TrackMania Nations custom maps on my pc to play them?

Hi

I just found games tracks i mean race tracks but I don't know how to install them . Thy are some abcd.gmx files and I don't know where to install them . there is no installation instruction.

You can download them from here :
Download TrackMania Nations Tracks, TrackMania Nations Downloads


And then :
1.) Download the track.
2.) Unzip the folder to a temporary one.
3.) Copy and paste the "trackname.gmx" (example name) to your Trackmania root folder. Standard would be:
"C:/Program Files/TrackMania/GameData/Challenges/Downloaded"
4.) in order to play the track open the game, select "Solo" and "Challenges" in the main menu. If you installed everything like said above the track will appear in the list.