Are you looking to sell or donate your Mac, or do you simply want to start fresh with a clean install of your operating system? Whatever your reason, there are a few different ways to erase your Mac and start from scratch. Here’s a step-by-step guide on how to do it:

1. Back up your data: Before you erase your Mac, it’s important to make sure that you have a backup of all your important files and data. This will ensure that you don’t lose anything important during the erase process. There are a few different ways to back up your data, including using Time Machine (which comes with every Mac) or an external hard drive.
2. Boot into Recovery Mode: In order to erase your Mac, you’ll need to boot into Recovery Mode. To do this, restart your Mac and immediately press and hold the Command + R keys. Keep holding these keys until you see the Apple logo or a spinning globe.
3. Erase your Mac: Once you’re in Recovery Mode, you’ll see a screen with a few different options. Click on the “Disk Utility” option and then select your startup disk (usually named “Macintosh HD”) from the list on the left. Click on the “Erase” button and then choose a name and format for your startup disk. Click “Erase” to confirm and begin the erase process.
4. Reinstall macOS: Once your startup disk has been erased, you’ll be taken back to the main Recovery Mode screen. From here, click on the “Reinstall macOS” option and follow the on-screen instructions to reinstall the operating system on your Mac.
5. Restore from a backup: If you backed up your data before erasing your Mac, you can restore it by clicking on the “Restore from Time Machine Backup” option in Recovery Mode. Follow the on-screen instructions to choose your backup and restore your data.

Erasing your Mac and starting from scratch can be a good way to troubleshoot problems or simply start fresh with a clean system. Just be sure to back up your data before you begin the process, as all of your files and settings will be erased during the process.