The way I understand it is, when you select a version you see exactly what the sheet looked like then, except it is in grayscale and the changes made between this version, and the next earliest version is highlighted in yellow.
So Scorpius has most of his powers filled in now, but if you select a version from two days ago, his power fields will be blank.
You cannot see two versions next to each other without opening a new web browser window.
The way to see what was changed in the highlighted area specifically would to select the next earliest version of the document.
At least that's the only way I know how to do it, but obviously, I learned allot of this very recently and I would be willing to a bet a creative person might find something I missed.