Recovery, in Android, refers to the bootable partition, in which the recovery console is installed.
It contains tools to help repair your installations as well as install official OS updates by using a combination of key presses or instructions from a command line sometimes.
Android is open, meaning the recovery source code is available, so that building a customized ROM is relatively easy.
1. Lets get started, press and hold power button to turn off your device.
2. When your phone is turned off you have to press and hold both Volume down button and power button at the same time.
3. When you will see LG logo on your screen you can release those buttons.
4. Once you did this there should apppear hard reset screen, similary looking like this:
5. Congratulations, you reached recovery mode on your LG Optimus G E975.
What does it for? In the past, a phone is more of a device used to make calls or text. However, it's much more than that.
Most Android devices are now defaulted with a fairly simple Recovery mode with features like Reboot System Now, Apply Update from ADB, Apply Update from External Storage, Wipe Data/Factory Reset, Wipe Cache Partition, Apply Update from Cache.
Just like a lot of other things with Android, even the Recovery Mode can be customized to do more things.