Select Reinstall OS X, and click Continue.
Here’s how to install (or reinstall) OS X, step by step: Boot from your Recovery HD partition by restarting your Mac while holding down the cmd+R keys. In this video, I will be showing you how to install Mac OS X Mountain Lion (10.8) on your Mac that is no longer supported by Apple using MLPostFactor. Download create-bootable-installer-for-os-x-el-capitan.sh to the USB drive. Download and Run install-mac-tools.sh in the USB drive.