If you make a git commit, and make changes to your model, then you’ll be able to see the changes since that commit in the commit view. You can open the commit view by pressing CTRL+V and then 1.
If you commit again and would now like to see the changes from one commit to the other, you can do that from the VCS log view. You can open the VCS log by clicking on the „9: Version Control“ Tab on the bottom left of your screen (Red 1 in the Screenshot) , and then on the tab „Log“ (2 in the Screenshot); or by pressing CTRL+Shift+A, typing „VCS Log“ and hitting return.
For small diffs, you may use the Icon to toggle the inline diff viewer at the right hand side (3b in the Screenshot). Make sure that „MPS model viewer“ is selected there (4 in the Screenshot).
For larger diffs, you may click on or press CTRL+D to open this diff viewer in a separate window (3a in the screenshot).
In this view, you may also diff between two versions that span a longer time. Simply click on the first commit, hold CTRL, click on the second commit, release CTRL and then right-click and „Compare Versions“ will show the models that differ between the two. Double clicking an entry there will show the diff for that model.
That’s a great illustration for why it is a good idea to have separate commits for every task or session, so that your history becomes easy to inspect.