Claying the heads

I might be the only guy on this forum that doesn't know but I doubt it.Would someone explain step by step the procedure for claying heads? Or suggest a book? Do you torque down head bolts or studs? Where do you buy clay,like an art supply store? Is the desired clearance on valves .50 and pistons .100? Do you measure the clay with a micrometer after compressing it? So many questions. Will someone have pity on the this ignorant soul?