From Online Manual
GUI Applications Mac OS X: SourceTree.app (Mac Store) (Its FREE for a limited time!) Tower.app (Paid) Windows: gitextensions tortoisegit Linux: ??
Tutorials Git Extensiosn Clone - http://www.youtube.com/watch?v=TlZXSkJGKF8 Commit changes - http://www.youtube.com/watch?v=B8uvje6X7lo Push changes - http://www.youtube.com/watch?v=JByfXdbVAiE Pull changes - http://www.youtube.com/watch?v=9g8gXPsi5Ko Handle merge conflicts - http://www.youtube.com/watch?v=Kmc39RvuGM8 A couple more Git clients:
Multi-platform (Windows/Linux/Mac) I've heard good things about: http://www.syntevo.com/smartgit/index.html (free for non-commercial use).
Multi-platform http://rapidgit.org/ (which is kinda... offline at this time. lol. Coincidences, coincidences.)
All are graphical clients.
For Linux: too many. For all tastes. :) Personally, I use the standard command line client, its little gitk interface, occasionally Git-cola, occasionally EGit (Eclipse plugin)... and I have several others of less interest. If you use PHPStorm editor, its Git plugin features can also be used directly for just about any simple and slightly advanced operations with Git.
More on Tutorials:
The "bible" - http://git-scm.com/
Interesting read (some may say it will help, some may say it will deter): an article presenting Git and SVN side by side and "translating" Git commands in the "equivalent" SVN commands. Interesting, and might make Git more approachable faster. Might also make slightly harder the switch from a "centralized" thinking to a "distributed" one, if I may put it this way. http://git.or.cz/course/svn.html
Tutorial, clear writing and to the point: (as usual from the author) http://www.vogella.de/articles/Git/article.html
More advanced features:
On submodules, you may find useful: (quick pick) http://book.git-scm.com/5_submodules.html http://chrisjean.com/2009/04/20/git-submodules-adding-using-removing-and-updating/ (a bit old though) http://joncairns.com/2011/10/how-to-use-git-submodules/
On git subtree, a very quick pick, merge subtree strategy: http://help.github.com/subtree-merge/