what is the g drive on my mac

What G drive?

Where are you seeing this G drive?

Unlike Windows, Macs don't have lettered drives.

Finder will show named Volumes and devices on the side panel.

Normally, you would see your computer's name and a "Macintosh HD" there under Locations.

Anything beyond that, was necessarily added by you in some way, so only you can know what that is.

Any external drives, USB drives and SD cards will appear there and may show a different name than what you are expecting.

The G-Drive would be an external hard drive that is connected to your Mac.

External drives are generally used for backups or extra file storage.