Ok i am new to unity ! and i want to learn how to make my own racing mmo but i don’t know anything about unity really …
i have been looking for video tutorials i found a few but they aren’t really helping so could someone help me get started ?
NOTE : I am 13 so i really just need basics on what to do. and i am making a racing game so i need to know how to make the track,cars and maybe avatar costomizing
thanks in advance ! 
Welcome to the forums. An mmo racing game eh? Good luck.
To start, you might want to look at this Car Tutorial
I would highly suggest you take out the mmo part of your idea. Stick with a racing game, just none of the networking. Doing a racing game is a large undertaking by itself, even more so with the networking involved in an mmo. If you finish and polish the racing game, then work on the mmo part.
Actually, if you finish and polish the racing game, work on networking. From there try the mmo.