Did you know that you could keep an OS on a storage drive, just in case? You never know when you might need to (re)install an OS on the go – I know I've had to. Below I'll explain how you can set up a storage drive with Mac's OS X El Capitan.
Click the Apple icon on your desktop, then click "App Store" to access your Mac Apple store. You'll be able to find the OS X El Capitan available for download in the store.
When the download is complete, the installation guide will start automatically. You'll want to prevent that. To do so, click the "menu installation" of OS X, then go to "finish installation" of OS X. That will stop the auto installation.
Connect an 8 GB or higher storage pen drive into the USB port. Then go to your search box at the top of your desktop and search "utility disk". Open Utility Disk – the app that appears from your search.
In the left-most window select the pen drive you've insert in your Mac. Then, on the right menu tab click "erase". In the format box click "Mac OSX expanded". Once you've you done that, click "Erase" again and confirm. This will format the flash drive for you.
When the drive is done formatting, close Utility Disk and open the terminal by searching "terminal" in the search box.
In the terminal window, copy the command provided below and press "enter". You'll have to enter the administrator password to continue.
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/OSX --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app –nointeraction
The command will then download OS X El Capitan onto the newly-formatted storage drive. But be patient! The process could take up to an hour to complete.
Once it's done, you'll have a copy of OS X El Capitan on a flash drive for future needs – whether you need to install it on a new machine, reinstall it on a current machine, or for whatever other reason.