I have a game where the car is how to make a rival who will be racing with me
That'll have to do with AI, or you can pre-make the rival to do certain rounds on the track...
AI, www.google.com has many examples of how to do AI, and you'll have to build this on your own, or you could use another persons AI sample, to help yours (Maybe waypoints you'll have to figure that out).
The other way, is, you could animate the enemy car to do the track like, 20 different ways, and of which, each has a dif. difficulty, so then randomly choose one, and have it run it that way... Problem with this, it'll be boring because then your just driving, you can't hit in to him or mess him up...
Hope this helps!