car script for unity

This all depends on your programming experience and what kind of racing game you want to make. If you want to do a classic 2D game, that is going to be a whole lot easier than something using 3D models and full physics.. So which type of racing game would you like to make?

You mentioned you were new to Unity, is this also your first time programming?

i wanna make a 3d racing game

If this will be your first project then you picked up a really hard challenge! In my opinion, implementing realistic car physics is a very complex task, that even a lot of AAA companies still can't do perfectly. I hardly doubt that you will find a script that is already implemented and fully working. I would recommend the following steps:

1. Read a lot about the Unity physics engine and try a lot of small stuff in order to understand how everything works. I don't know how much knowledge you have about physics so you might have to learn a couple of theory topics in order to understand enough. Yes, Unity has its own Physic engine but if you are now using everything correctly you will not get good results.

2. If you feel confident enough start with a small prototype and try to implement a simple physics-based input controller. There are a lot of different examples of these types of input controllers. Test a couple of them and try to modify them to your needs.

3. Try and error until you feel happy about your results. As I said, in my opinion, this is a pretty rough idea and especially as a beginner that really can take a lot of time.

Sadly I can't really give you more tips because I have never done such a project myself. I just know from my own experience that a lot of physics-based stuff is pretty hard to get into. Please don't think that I want to discourage you. Nothing is impossible and Unity is a very good engine to get started! I would recommend to try out what I have said and if you have more specific questions feel free to ask again. In that case, it should be easier to help you.

i'm very thankful for your help mr Znippy