erase all content

Depending on why you want to erase, and which MacBook Air…

… What to do before you sell, give away, or trade in your Mac - Apple Support

… Use Disk Utility to erase an Intel-based Mac - Apple Support

… Use Disk Utility to erase a Mac with Apple silicon - Apple Support

On an M1 MacBook Air you can also use a second Mac with Apple Configurator 2 and do a restore which will entirely wipe the internal drive and restore Big Sur or Monterey to it as if it were a new machine.

If MacBook is 2018+ year upgrade to Monterey and simply Erase all content and settings it is very simple.

This is the best way for 2018+ MacBooks