The "method" is to turn one or more burners off and place the food over the cold burners. The temperature varies depending on what you're cooking. It is impossible to say how many burners should be on or what teir setting should be. The objective is to maintain a specific temperature, and it is strongly affected by the outside temperature, wind and variations in a particular grill. Possibly even by the phases of the moon and position of the planets
. The only way to do it is to have an accurate thermometer and use it. One tip: it takes a few minutes for adjustments to take effect, so wait between changes o see what's happening.
As for temperatures, I cook beerchicken between 325 and 350 for 45 min or so, until internal temp of thigh is 175. I find 180 to be overcooked. Let it rest for 10 to 15 minutes before carving.
It sounds like you're a newcomer to grilling, so I'd suggest getting a Copy of Steve's book How to Grill, or another basic grilling cookbook.