How do I wipe my Mac and reinstall OS?

Select your startup disk on the left, then click Erase. Click the Format pop-up menu (APFS should be selected), enter a name, then click Erase. After the disk is erased, choose Disk Utility > Quit Disk Utility. In the Recovery app window, select “Reinstall macOS,” click Continue, then follow the onscreen instructions.

How do I get my operating system back on Mac?

Enter Recovery (either by pressing Command+R on an Intel Mac or by pressing and holding the power button on a M1 Mac) A macOS Utilities window will open, on which you will see the options to Restore From Time Machine Backup, Reinstall macOS [version], Safari (or Get Help Online in older versions) and Disk Utility.