i use sourcetree, and i like it a lot, but with all the positive talk about magit, i need to try it
i now only use emacs for org-mode and this mode is also by far the best personal todo list i used (i.e. if you dont need any social, sharing features found in web todos, org-mode is the best there is) .. so i know emacs can be very good
I can't remember if I read any specific documentation, but Magit has pretty good integrated help.
Type M-x magit-status to launch it. This will show your git status. Then type ? to see what you operations you can do.
In general, things just work as expected. Bind "C-x g" (or whatever) to open the status window, and "s" will stage changes. "c" will bring up a window asking if you want to commit. "k" will kill whatever the point is at. Tab will expand changes, and you can highlight then with a region to stage just part. (Or kill to discard part.).
At any time "h" provides a ton of help.
http://endlessparentheses.com/it-s-magit-and-you-re-the-magi...