They both eat fruit and leaves. Also they both live in tropical areas.
Dude - the gorilla IS an ape!!
Apes are smarter, they have opposable thumbs while some monkeys dont, apes have no tails and they are bigger. Thats all I know.
Monkeys have tails (DeBrazza's Monkey, Black Howler Monkey, Drill monkey), apes (Gibbons, gorilla, chimps) do not.
From what I've read, two of the main differances are that monkeys are generally considered intelligent, and unlike apes, they usually have tails. (according to wikipedia)