In order to perform a manual Time Machine backup, you simply need to click the Time Machine icon in the top-right menu bar, and then click Back Up Now:
If you do not see the Time Machine icon in the top-right of your screen, you can enable it by following these steps:
- Open System Preferences by clicking on the Apple in the top left, followed by System Preferences
- Click Time Machine
- Click the Show Time Machine in menu bar checkbox in the bottom of this window
