Unplug the lamp you want to control with the outlet dimmer switch.
Put the outlet dimmer's plug into your electrical outlet. Uncoil the cord with the dimmer switch connected to it and place it on a table or other location near the lamp you want to control.
Plug the lamp into the outlet on the back of the outlet dimmer's plug. Turn the lamp on. Control the amount of light with the slider control on the dimmer.