Facelets itself has an excellent getting started document:
Then there several JSF-related documents you need to know and understand:
As to the JSF implementations and component libraries, there are two (major) JSF reference implementations: Sun Mojarra and Apache MyFaces. When you want to use JSF you need at least one of them (not both or more). At the moment I can recommend Mojarra above MyFaces.
Then you have many JSF component libraries which you can add on top of any JSF reference implementation. The component libraries usually adds just that extra flexibility (e.g. Mojarra Scales and Apache Tomahawk) and/or ajaxability -often also in combination with skinnability- (e.g. Apache Trinidad, JBoss RichFaces and IceFaces). You can in theory use as many component libraries as you want in a project, but mixing skinned/ajaxified libraries is generally not a good idea because of potential collisions in lifecycle, viewhandling, javascripts, etcetera.
Good luck.