Greetings!
Fortunately, there is a wealth of information available online about this topic. I'm not sure what class this is for, so I don't know how technical you are supposed to get, as far as the bioliogy of the disease. If by "causes" you mean, scientifically speaking, you'll want to talk about how the disease acts in the bloodstream and how it manages to defeat the body's immune system. If by "causes" you mean, how is the disease transmitted, you may want to approach it from a more sociological perspective.
Try doing internet searches using such search terms as "HIV transmission," "HIV causes," "HIV treatment," and see if you can narrow down the information to your specific questions.
Once you have enough information for a rough draft, I'd be happy to help you with editing! If you need more assistance before then, please let me know what type of help you need, a bit more specifically.
I hope this helps!
Thanks,
Sarah, EssayForum.com
Sarah, EssayForum.com