I’m about to start building a game that’s sort of a racing thing, and I was wondering that after I build the track in 3Ds Max … how am I going to define the track and the boundaries and all that? is it through scripting?
I’m assuming when you say define the track you mean collisions?
When you import the track model you can use a Mesh Collider so that it interacts with objects. For the boundaries (I take it you mean walls etc.) you can use the same technique to generate the collision mesh from the models you import.
If you need invisible walls you can either create a GameObject, attach a box collider and position them around the track, or create a model and use that as the collision mesh.
There is a fantastic free Racing Game example on the Asset Store, I suggest you download it, poke around and see how everything was created.
What I meant is that I want Unity/My game to know that this mesh is a racing track and the car should move on the black asphalt only!
Mr. Adam I guess that’s what I was looking for! that makes sense, I can define the walls of the track as a game object that has a Mesh Collider! and whatever object within this Mesh shouldn’t be able to leave!
I have checked that free racing example but I’m new to Unity so I still don’t know how to figure what and where 
but I’m learning 
thanks.