Can someone tell me what pure Communism is in a nutshell?

Just curious. I don't want to just accept the system I've grown up under here in America rather than learning what else is out there, and I want to get an UN-BIASED account of what Communisms goal is, how it seeks to accomplish this and what the pro's and con's of a pure communist system are. I realize there are variations of communism as well, if anyone wants to expand on those as well, that would be great.