Treat the contractor like everything else in our world. It's a switch.
you have A1 and A2 which is your coil contacts. And usually you have 1,3 and 5 which is your "feed" at the top of your contactor and 2,4 and 6 which is your "load" at the bottom. Your A1 is usually your live of your control and A2 your neutral.
It all depends on what your using it for, and location etc as to how you wire it.
Fr example if your wanting to switch a bank of lights and they are controlled via a local photocell, the photocell would be wired via A1 and A2 so when the photocell closes (as its just a switch like everything else) it will send voltage to the coil energising it and pulling in the contacts allowing your lights to switch on.
If you have 3 separate circuits you want to switch then you will have 3 breakers controlling your lights and a control circuit controlling the photocell.
You get lots of different types of contractors so make sure and get the right one for the job, ie normally closed/ normally open/ coil voltage is it dc/ac etc
but as everyone has already said, pop the search in to google and look for images. It's basic wiring and fairly straight forward.
