Easy to handle, this editor allow you to create a track with the use of the mouse, unlike external track editors.
How to use it ? Simply click on the chosen track element on the right and put it on the left main screen to put the element on the track. You can switch between the different categories of track elements with F1 to F10 keys or with the mouse by using the white bar below track elements. You can also edit the terrain (hills, water) by using the SHIFT+F1 keys. This feature is not written in the game manual but is very useful to be known if you don't want to always race in one of the 5 default terrains of the game.
A documented, but not widely known feature is that you can check the validity of the created track by pressing the C key. This validation is performed the same way when you select driving on the track from the main menu. If the track is invalid, a message is displayed and the cursor moves to the element where the validation failed.
The in-game track editor is one of the reasons (and probably the most important one) that allowed Stunts to have such a long life and an active community among the years. If Stunts had no track editor, this wiki would have probably never existed. How many racing games were quickly forgotten just because they had a short life due to a small amount of available tracks? Stunts is not like that, thanks to this track editing tool.
But such a tool is not always a key to success. A game similar to Stunts, also created in the beginning of the 1990's, named Hard Drivin' and its sequel Hard Drivin' II, also had an in-game track editor. But it was such a mess to create a valid track that this game never managed to have Stunts' success.
In-game track editor has 2 inconvenients : it doesn't show a full view of the track you create and it doesn't allow any bug as the game engine has some strict limitations. This is why some external track/terrain editors were created by Stunts fans.