First, cut off the inflow of electricity by turning off a switch. Next, unscrew the bulb that burnt out and put it aside. Take a new bulb out of a box and screw it in by turning it in a clockwise direction. Make sure that you screwed the bulb in correctly and turn on a switch. If the bulb does not light, turn off the switch, unscrew the bulb and make sure it is not burnt out. If the bulb is ok, screw it in again and if it is burnt out, take another one.