Positives and Negatives of smoking weed?

I'm 15 years old, it's summer time, and I'm coming to a point where im really curious about things like weed. A lot of my friends smoke it and i'm offered it quite often but never tried it yet. I'm not stupid enough to do any other more serious drugs or anything like that, and it's not a peer pressure thing, I have no problem saying no. I just want to try it so please give me the negatives and positives about smoking weed, and please only answer if you know what your talking about.