The switch is in the upper corner of the schema. The fact it has four pins is for mechanical stability, but it is just an on off switch. The witch you provide is a ON/ON switch, either left or right is connected. You need to use the middle and the left pin of your switch. The right pin can be left not connected.
BTW, the switch pictured is a panel-mount. You drill a hole in a panel, stick it through, and secure it with the included nut tightly. That's the only way it will work, stable enough, besides connecting it. You can also buy sliding switches for PCB through holes to easily prototype on a breadboard.