Uhm ok, this is top secret (that's why i'm writing it online)?

well, i'm 15 and i've never smoked weed though my friends do about once a month. (i'm the youngest in the group, the oldest is 18) well anyway, on saturday my friends are having a party and thy're planning to smoke weed, they invited me and i'm going to go as always, but i don't know if i should smoke too.. i kinda want to try, but i want all information that could be useful: how bad it is for you, what are the immediate effects and the long-term ones and what can happen if i am discovered. I REALLY don't know what to do, but if been friends with these guys for years and i know tey would never force me to do something i don't want to do..