Strip the end of the non-metallic sheathed (NMB) wire and connect the ground wire (bare copper wire) to the ground buss. Connect the white wire to the neutral buss.
CAUTION! Before connecting the black wire to the breaker, make sure the breaker is in the OFF position. Now, connect the black wire to a 20-amp breaker or fuse. Mark the panel schedule with the placement location of the breaker you connected to.
If there isn't a spare breaker, you can either add a breaker or connect it to an existing circuit that doesn't have much connected to it.