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. If you want to start the whole process make sure your device is switched off, if it's not then please hold power button to do so.
2. Now hold down Power button and Volume down button at the same time.
3. After a moment there should appear LG logo, when you will see it, you can release buttons.
4. Wait few seconds and there should appear Recovery mode menu, good job!
5. To navigate use your volume buttons and power button to select.