1, "2 holes a screw locking" for a terminal, a terminal into the fire (switch disconnected with an electric pen to test the one with electricity), a terminal out of the fire (directly connected to the lamp head of the line).
2, there are 3 wires in the switch box, must be clear to connect. General family switch box, because to connect the socket, so, inside the fire line (generally red, neon tube glows when the electric pen test), zero line (generally blue or black), ground (specified as yellow and green two-color line).
3, one end of the switch into the fire, one end out of the fire (note that 2 are fire oh), out of the fire of the line can not be connected to the zero line or ground, otherwise the switch is open on the short circuit. Judge the line out of the fire, to use a multimeter with a piece of wire (do not be afraid of trouble, be sure to confirm, or the consequences are serious), with the multimeter's resistance file to confirm that the switch out of the fire of the line, and the head of a line is through, in order to be wired. Be sure to disconnect the power when testing.