to format your hard drive for your mac
plug in your drive and open finder
in finder click applications
scroll down to utilities
choose disk utility
in the pane on the left of the disk
utility window
click the drive you want to format
at the top of the window click erase
choose the file system you want to use
usually you'll want exfat
which is the default for mac os but can
also work on pcs
now click erase