Apple hosts the El Capitan installer on their servers. You can typically find it on the Apple Support page titled
Open Terminal and paste the following command (assuming your USB is named "MyVolume"): sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app System Requirements Mac Os X El Capitan 10.11.6 Installer Dmg Download
Released in July 2016, version 10.11.6 was the final "polishing" update for El Capitan, focusing on security, stability, and compatibility. Here is everything you need to know about downloading and installing it safely today. Why El Capitan Still Matters Apple hosts the El Capitan installer on their servers
The "Install OS X El Capitan" app in your Applications folder. focusing on security