Each revision is shown in reverse chronological order with a timestamp of when it was created and the Workflow state it represents, either Draft, Published, or Archived. On the right side of this list are radio buttons which allow you to select two revisions and a button below to compare the revisions. You can also choose to Revert to a particular revision, which will make that the current state of the content.
Comparing Revisions
By selecting two revisions and clicking the Compare selected revisions button you can view the differences between those changes.
Content which was removed will appear in red and content which was added will appear in green. There are several view modes available. See below for some examples.
Pictured above: the Visually Inline view mode for revision comparison.
Pictured above: the Unified Fields view mode for revision comparison.