CyanogenMod is a custom android rom for you android device. CyanogenMod extends the functionality of stock Android allowing for more customization and modification. Depending on your android device it may not be required to be rooted to run the installer. CyanogneMod can be installed through a manual process very similar to any other mod. Instructions are listed on CyanogenMod Website. If you have a nexus device such as nexus 5 or nexus 7, plug your device into the computer and go to the installer page. The web applet will guide you through the process. Once you have completed the install process your device will be rebooted, rooted, and have CyangoenMOD as the primary ROM.