all the double arrows with +12V are wired together - there are 4 of them. it's a way to avoid having a gazillion lines all over the place. just like ground (there are 4 ground connections, too). so, the switch turns on power to the entire circuit.
note, pin 7 doesn't connect to +12V, it goes through the resistors/trimmers.
by the when you get it all wired together, set the two trimmers at about the half-way point. that should be pretty close to a reasonable pulse rate and duration.