This is my first time selling a car so bare with me

-Do I have to file tax at the end of the year in regards to the amount I got from selling the car?
-Is it beneficial for me to put it as a higher cost or lower cost? For instance I'm selling it for 8k, is it beneficial for me in any way to put it on the Bill of Sale that I sold it for 7k or 9k?
-I just need the title and Bill of Sale to complete the transaction correct?