How to "properly eject a disk"

1. Drag the disk's icon on the Desktop to the Trash.

or

2. Click the icon once to highlight it and hit command-e

or

3.Open a Finder window with sidebar showing; your disk should be listed under 'Devices'. Click the up-arrow-with-a-line-under-it to eject.

What you mustn't do is just turn off or disconnect a disk without doing one of the above - this can lead to data corruption.

Having ejected the disk you should leave it for a few seconds before disconnecting. A USB stick will often go on flashing for a short time after disappearing from the Desktop and you should wait until this has stopped.