Been discussed a few times. Did you try a search?
Basically, remove the large vacuum tube from the brake booster, and pour 1/2-2/3 of the container into the intake manifold via the tube, with a rate that's just slow enough that the engine won't stall. Turn the engine off when this is done to allow the Seafoam to do its work inside the cylinders. Pour the rest into the oil. Some people also pour some into the fuel talk. Wait 15-30 minutes, then start it back up again, and prepare for the neighbors to call the fire department because the exhaust will send out a MASSIVE plume of white smoke like your house is on fire.