Anime Terms. What are they really?

I have been liking anime for a few (6) months now and I am still quite new to the terms being used. Terms like Tsundere, Yaoi, Yuri, Uke, Moe, and others I still probably don't know. What are their exact definitions, what are they for, why were they made? Although I have an idea about some of the terms I have mentioned before, I am quite curious about Yaoi and Yuri. My older sister says it has something to do with pairings, yet why are they even existing? Are they just for the tastes of Anime fans? To answer here you must define and explain why that certain term is for. You can do them individually or by group. You can even add additional terms I may not know yet or have forgotten to add here. Oh, and please no cussing and answer properly and only answers are accepted here. This is also for other Anime fans so that they can understand the World of Anime better.