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. The whole operation start from turning off your device, so hold down your power button to turn it off if its on.
2. Next step is pressing combination of three buttons and holding them down. So press Volume down+Home+Power buttons.
3. Hold them untill you see LG logo and wait few seconds.
4. Now you should see Recovery mode menu, good job!
5. To move highlighted area here use volume buttons "+" is for up and "-" for down, and to confirm press Power button.