If you’d rather install Yosemite on the SSD then follow the How to Install Yosemite on a New SSD guide. Here’s link to a video on how to physically install the SSD as well as run the software installation. Follow the prompts until El Capitan is installed.Choose to Install OS X on the formatted SSD.Set the Format type to Mac OS Extended (Journaled.) Click on the Apply button, then wait for the Done button to activate and click on it. Click on the Erase icon in Disk Utility's main window.
Create a bootable image from the El Capitan installer on a USB stick larger than 6GB.It will be downloaded to /Applications and be named Install OS X El Capitan.app It might complain that you already have it installed but download it anyway. Check compatibility Make a backup Get connected Download OS X El Capitan Install the macOS installer Begin installation Allow the installation to complete. Download El Capitan installation from the App store.