After downloading El Capitan USB from this page, download El Capitan from the Mac App Store.
Start El Capitan USB, and all you need to do is to select the USB device on which you want to install El Capitan.
After few minutes, if all goes successfully, you are ready to run your clean installation!
The interface is simple and intuitive. With a single click you can create a bootable USB of El Capitan.
El Capitan USB automatically check the required disk space and warns you if it is insufficient.
The app will format your USB device in the "Mac OS Journaled" format and will copy all the files needed to boot from the device.