how do I back up my MacBook Pro using a G external hard drive?
How do I use a G external hard drive to back up my MacBook Pro?
MacBook Pro 15″, macOS 10.15
Use Disk Utility to format the drive (APFS/GUID options for macOS 10.13 and up). You should then be prompted to use it for Time Machine backup, but if not select it in System Preferences > Time Machine.