As an admin (or rollbacker), you may spend much of your time reverting changes made to pages. You may be familiar with the undo feature, which undoes the last edit to a page, and manual reverts, which allow you to revert to any edit of a page by opening any page history revision, clicking edit, and saving. As an admin (or rollbacker), you also have the rollback feature, to expedite the process. It's important to note that a rollback requires only a single click to revert one or more edits. There is no confirmation after the link is clicked.
Use of rollback is subject to the rollback guideline, which explains when rollback can be used, when it cannot, etc. In summary, it should not be used for edits that were made in good faith (even if problematic). Misuse of rollback may lead to the removal of administrator (or rollback) privileges.