A bootable USB can be useful if you want to install Mac on multiple computers without downloading the installer each time, or when you can't install using Mac Recovery or the other methods. Maver-ick -s, Yosemite, El Capitan, Sierra, High Sierra, Mojave, Catalina, Big Sur (Current). What's in the box? (1) 64 GB 3.0 USB with 8 items (1) Extensive Booklet (1) Technical Service/Support Instructions: Regular Intel Macs: 1- Shut down or turn off the Mac. 2- Connect the bootable installer to the Mac. 3- Turn on the Mac, then immediately press and hold the Option (Alt) key. 4- Release the Option key when you see a dark screen showing your bootable volumes, including the bootable installer. 5- Select the compatible bootable installer. Then click the onscreen arrow or press Return. 6- Choose your language, if prompted. 7- Select Install Mac from the Utilities window, then click Continue and follow the onscreen instructions. Instructions for Mac with Apple Silicon: 1- Shut down or turn off the Mac. 2- Connect the bootable installer to the Mac.. 3- Turn on the Mac and continue to hold the power button until you see the startup options window, which shows your bootable volumes, including the bootable installer. 4- Select the compatible bootable installer, then click Continue. 5- When the Mac installer opens, follow the onscreen installation instructions.