OS-X 10.11 El Capitan installation media USB on Mac

Use the DiskMaker X application for the simple automated way.

1. Ensure you have installation media downloaded.
2. Use the diskmaker X application

http://diskmakerx.com/

 

Full details:
http://mac-how-to.wonderhowto.com/how-to/create-bootable-install-usb-drive-mac-os-x-10-11-el-capitan-0162371/