The new Version History, which is accessible from File menu as well as the Review tab, opens up a pane on the right side that displays the versions/revisions of the spreadsheet with the most recent ones on the top. You can see the timestamp when it was created as well as the users who had contributed to that version. Clicking on a version will load that version of the spreadsheet with the changes automatically highlighted with colored lines at the top of the modified cell. Each collaborator on the spreadsheet is given a color and the changes are highlighted in that color. You can also view the list of changes made in a particular version by clicking the 'Changelog' link beside the selected version on the right side pane. The screenshot inserted below should be self-explanatory. Click on the image to view it in its original size.

We maintain the recent 100 auto-versions as well as all versions that have been created manually (using File > Create Version). With this release, you can also Name a Version that was automatically created. This will be helpful when you want to refer to it at a later date. And versions that have been created or named manually will not be deleted automatically. They will be maintained unless you explicitly delete that version or delete that spreadsheet itself.

Audit Trail: