You'll see the MacOS Utilities window choose 'Disk Utility.' Now you can choose to erase your startup drive, and choose 'Mac OS Extended (Journaled)' as the operating system. To get around that problem, hold down the Command + R keys when you turn on your Mac and let go when the logo appears.
If you want to format your Mac's system drive, you can't do that when the Mac is running normally because the drive is in use by the operating system. This is useful if a drive is being used under both Operating System (OS)to. Usually, you'll want ExFAT, which is the default for the MacOS. A Western Digital external hard drive can be used on both Windows and Mac OSX. Select the drive you want to format and then choose “Erase.”Ĥ. At the top of the window, click 'Erase.'ĥ. In the pop-up window, choose the file system you want to use.