"Nevertheless" is usually used to start a sentence, and it has a similar meaning to "however." But "nevertheless" has more of a feeling of being in contrast to all the things that were just said, while* "however" just means that at least one thing doesn't agree. Like, if I spent 30 minutes listing all the things my sister has messed up recently, after I finish, I could say, "Nevertheless, she's my sister and I love her." But if all I had said was, "Sometimes, my sister doesn't clean her room," then I'd follow it up with, "However, she's my sister and I love her." "Whereas" is a conjunction. I put a * up by the word "while" in the last paragraph, because I actually typed "whereas" there and then realized I shouldn't use a word I hadn't explained yet. Like "while," "whereas" means that two different (but possibly similar) things are both true at the same time. I think it would be most useful to compare it to "but." "But" is a coordinating conjunction, and it is used to combine two things which are contradictory. "Whereas" is a subordinating conjunction, and it is used to combine two things which are contradictory, but kind of "go together." I tried to think of a good example sentence but couldn't. If you need one, let me know and I'll try harder. "Whereas" is also often used in documents like laws, to mean "because." For example (this is totally made up, real laws are way more serious and also more real): "Whereas this legislature is convened on this day March 30, 2015, and whereas we are lawmakers, and whereas our job is to pass laws, we hereby pass this new law."