Witnessing is telling others about the Lord so that they will come to the Lord also.
The one book that really changed my heart about witnessing was Hell’s Best Kept Secret by Ray Comfort. I want to encourage you to read it, too. The younger you are (as a Christian), the more important it is to read it.
If you are looking for tracts, you can print some free tracts from this site or you can purchase tracts from my favorite place, Living Waters Publications. They have some of the best tracts in the world! What is cool is that they are so unique, that, with some of them, all you have to do is ask someone, “Did you get one of these?”
May the Lord richly bless you!