I learn in a very top-down way - I'm not initially detail-oriented. First I want to know the big picture, the overarching ideas and the big levers that you pull with all your might. I prefer to understand the screws and springs after I've grasped the big things. These are the result of my screws-and-springs research.
Disclaimer: I'm still a relative git newbie, although I have been using it for serious work since March, so you should verify what I say before going to town on your repositories. Also, I am doing my best to 'umm' and 'aah' less on these :-)
This video explains the interaction between commits, branches and branch heads.
This video graphically explains what the git "fast-forward merge" feature does. This is a special-case operation in which you branch off a commit, work only on the new branch and then merge back. Compare this video to the one above in which
NewFeaturewas branched and work continued in parallel on both
This video contains a slight error around the 2:00 mark that is noted in the Viddler timeline.
I would appreciate feedback on whether you find these useful.