2006 Ford Explorer

Basically, use a small chisel to remove the old plug. Make sure not to damage the engine block. After that, a new plug just is tapped into the hole. They make two types, an all steel, and one that is rubber / steel. If you have little access, the rubber one simply presses in and there is a bolt you tighten to expand the rubber component of the plug. They are easier to use if you can't get a hammar / flat piece of wood into the area to tap it in.