Click on the “Summary” tab on the menu on the left side of the window. In the right-hand portion of the iTunes screen, you’ll see a “Back Up Now” button. Click that. The backup should begin.
The progress bar at the top of the screen will display the progress of your backup. The backup could take anywhere from a few moments, all the way up to several minutes to complete. The amount of apps and data you have stored on the device will determine the length of time it takes to complete. Once completed, the time and date of your last backup will be updated. (You can see this below the “Back Up Now” button.
This was a rather short how-to, but it could come in handy if you’re faced with the need to quickly backup your iOS device and don’t have a Wi-Fi signal available. And it’s always a good idea to have multiple backups.