I am trying to wrap my head around the Revision Graph provided by TortoiseGit. How exactly is it related to the Graph from the git log command? For example, I don't understand why the arrows are pointing away from the first commit instead of pointing towards it. As far as I understand, it won't even show the whole log but instead just the latest common commit from where the branches go off?
The revision graph is a visualization of the output of git log --simplify-by-decoration - it shows all branches and tags and should provide a rough overview over the branching structure. TortoiseGit 2.8.5+ will also allow to display all branchings and mergings.
The direction of the arrows has no specific meaning here and will be adjusted to the Git meaning (pointing to the previous commit) with the next release.