Android recovery is a dedicated partition, with tools that will help you repair/recover your device, clean caches, run updates from SD card etc. You can get into recovery using a key combination specific to your phone manufacturer and model.
Turn your phone off.
Press and hold Vol- and Power at the same time.
When the screen of your Lg Optimus 3d p920 flickers release all buttons and wait. In a few seconds the recovery ui will appear.
Sometimes the method we described above does not work. In that case try the following instead:
Turn off your phone/tablet.
Wait a few seconds
Press and hold the Vol- and Power Button at the same time for a few seconds until the LG logo appears.
Release the buttons and hold them again until you see the recovery ui