Review (Manual Approval)
The review tab will appear if you have Manual Approval activated for your database.
See Tuning Options for how to enable Manual Approval

Applying / Skipping a recommendation

When it is ready, the Review tab will have a red icon indicating a recommendation is ready for review. On the lower portion of the panel you will be able to view the new recommendation and compare it to your current configuration. Buttons to either skip this recommendation or apply the recommended changes are in the top right.
To manage the email notifications you receive when recommendations are ready see Unsubscribing / Resubscribing from emails.