RE: 509 flasher

I have looked at the above 100 times and I'm still confused. I don't really want to build this circuit without understanding it. I really hope somebody could help with this one. I'm not familar with the Hot in - Hot Out -Return (White). When I see White I know what that means. So which of the hot in and hot out is supposed to be the black? Is the green wire used? Does the load hook up between the Hot Out and the Return? What is Vcc supposed to be? Is this where I hook up the load? What is RV1? As you can seem I'm not an electronics wiz, but understanding this would help out greatly. As you can read, I'm really lost.