Conservation of Mass?

Ok. This week, all I can remember seriously learning was the conservation of mass, and a bit about alpha, beta, and gamma decay. And we talked a bit about nuclear fission and fusion. Then, the next thing I hear is that we have a Test on Monday! WHAT!? Oh no! What have we actually seriously learned. Gosh, I don't know what to do! Seriously, WHAT HAVE WE LEARNED? Well, wish me luck! :(