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 anda must define and explain why that certain term is for. anda can do them individually atau sejak group. anda can even add additional terms I may not know yet atau have forgotten to add here. Oh, and please no cussing and answer properly and only jawapan are accepted here. This is also for other Anime peminat-peminat so that they can understand the World of Anime better.