Step 1: Prepare the required tools and files

- A Mac computer (can be any model)

- A USB flash drive of at least 16GB (make sure that there is no important data in the flash drive as it will be formatted)

- An image file of the Mac operating system that you wish to install (usually in DMG or ISO format)

Step 2: Format the USB flash drive

On your Mac, open the Utilities folder in the Applications folder, and then open the "Disk Utility application. Select your flash drive and click on the "Wipe" tab. Make sure to select "Mac OS Extended (Journaled)" as the format and name the flash drive. Click on the "Wipe" button to format the flash drive.

Step 3: Create a bootable USB flash drive

Download and install "macOS Installer", an official tool for creating bootable USB flash drives. After opening it, select the version of Mac OS you want to install and click "Continue". Select your USB flash drive as the destination disk and click "Continue". Next, the tool will copy the installer files to the USB drive, a process that may take some time.

Step 4: Restart your Mac computer

Make sure the USB drive is connected to your computer, and then restart your Mac. during the restart process, press and hold down the Option/Alt key until you see a screen displaying the available boot options.

Step 5: Select the USB drive as the startup disk

Select the USB drive as the startup disk from the startup options screen. Once you have selected the USB flash drive, click "Continue".

Step 6: Install Mac

Your Mac will boot from the USB drive and the installer will be displayed. Select "Continue" and follow the prompts during the installation process. You'll need to select the appropriate installation destination (usually your Mac's internal hard drive) and click Install. The installation process may take some time, depending on the performance of your hardware.

Step 7: Finish the Installation

Once the installation is complete, your Mac will restart and display the "Setting Up Your Mac" screen. Follow the instructions to complete the initialization process, including selecting a region, language, network settings, and more.

After reinstalling your Mac, you can restore your data or reinstall the applications you want. Remember to transfer your previously backed up data or important files to the newly installed system.

Remember, always back up your important data before performing any system operation just in case. Also, you can find more detailed instructions and video tutorials on the official Apple website.