well the wiring up is simple, there are lots of easy to follow wiring diagrams on the net but basically a relay is just a simple switch, be it one you can control from a external trigger... ie. a on off switch in the cab or from the stalk if you are going to get one with that switch. so you would wire in a live feed to the fogs with a inline fuse, then run the negative feed through a relay and back to the lights, then run a trigger line to the relay from a switch where ever you want it... the more pain in the ass process is wiring in the actual loom, not much space in the engine bay and digging around under the dash can be fun to lay new wires... however if the loom for the fogs is already in place I suggest you make use of it, sometimes the loom isnt finished and needs a fuse or a relay put in, sometimes everything is already there... you will need to see what is there...
put a few beers on the line and someone will be around to help if you need it