I need some help for a mock trial in class.

I am supposed to write a direct examination for a man by the name of Farley on the plaintiff. I read on the internet that direct examinations are conducted by the attorney on the witness's side. But I also read the goal of the direct examination is to produce evidence...this makes it sound like you're trying to incriminate the witness. Why would the attorney on the witness's side try to incriminate the witness? What is the purpose of the direct examination then?