How to Block People on Yahoo?

ok, i recently got an IM from a woman named Marissa Garret. I don't know her, but I wanted the messeges to go away. I added her, asked her who she was in case i did know her. it turns out that her name is roxy and i think she's a star. she asked me if i ike big chests or behinds. Itold her that i am only 14 and a girl. this is disgusting, is there anyway that i can block this person?