Working with Finder
When you connect a flash drive or external hard drive to your Mac, it is known as mounting the drive. Before you disconnect the drive, it's important to eject it (or unmount it) properly to avoid damaging the data.
If your flash drive appears as an icon on the desktop, right-click the drive icon and select Eject. The drive icon will disappear from the desktop. Alternatively, you can click and drag it to the Trash. It can then be safely disconnected from your computer.