People have basically answered your first two questions, but I feel like a little more could be added on the one above.
Deaf humor and hearing humor are VERY different. Humor, in almost every language, is mostly a play on words. People can use a phrase that has like three different meanings, or that SOUNDS like another phrase. The context of the joke and conversation can make a meaningless phrase like "do it" and have it mean a million different things depending on what else has been said. American English humor uses A LOT of sarcasm, so something can be said that by itself sounds innocent, but the WAY it is said makes it mean, sad, funny, etc. Deaf humor uses play on words as well, such as "please but" in a joke about trains, talking about the guard rails at a train crossing needing to be lifted.
Okay, I'm not real sure if that was clear, but maybe someone else can word it better.
Any other questions, PLEASE ask, I am always willing to answer! I am happy to know some deafies actually have questions about hearing culture and I am not the only one with questions about deaf culture!
okay, adios, Kelsey