Break the stems off the chiles and toast them until they are fragrant. To rehydrate, I use very hot tap water, not boiling, as that removes too much of the flavor. Soak only long enough to make them pliable, usually 20 minutes, again, as soaking too long will weaken the flavor. I usually discard the soaking water, but you can taste it first, and if it isn't bitter, use it as part of the cooking liquid. The chiles are now ready to be chopped or pureed for use in recipes.
Chipotle powder is used like any other chile powder to flavor rubs, sauces, chili con carne, etc.
Remember, however, that powder retains full flavor and punch, so use it with caution. If powder isn't available you can make your own from whole pods by using a spice or coffee grinder. The chiles must be very, very dry, and if your pods are still pliable, toast them on a comal or roast them in the oven. If you are using a coffee grinder, first grind uncooked rice or soda crackers to remove the coffee oils and residue. Repeat after grinding the pods, unless chipotle flavored coffee appeals to you.