This answer is great for seeing a visual diff between two files that are checked into git: How do I view 'git diff' output with a visual diff program?
Howev
Here is how to see the visual diff between whole commits, as opposed to single files, in Visual Studio (tested in VS 2017). Unfortunately, it works only for commits within one branch: In the "Team Explorer", choose the "Branches" view, right-click on the repo, and choose "View history" as in the following image.
Then the history of the current branch appears in the main area. (Where branches that ended as earlier commits on the current branch are marked by labels.) Now select a couple of commits with Ctrl-Left, then right click and select "Compare Commits..." from the pop-up menu.
For more on comparing branches in the Microsoft world, see this stackoverflow question: Differences between git branches using Visual Studio.