The garage is an unconditioned space in your house and doesn’t need to be thoroughly insulated. However, to keep the rest of your home comfortable and energy efficient, you need to insulate the wall or walls that separate the garage from the rest of the house. This is the case whether you cover the walls with drywall or leave them unfinished.
You insulate them as you would any exterior wall, with insulation that includes a vapor retarder. Before installing insulation in garage walls, clear the area inside your garage of any obstacles.