Countersink: A hole with the top part enlarged so that the head of a screw or bolt will lie flush with or below the surface
Countersinking is easy to do and is used to hide the heads of screws for appearance, or for screwing two pieces of wood together when your screws are too short.
To do this, find a drill bit that is the same size or slightly larger than the head of your screw
With the drill bit, drill your hole as far down into the wood as you want the head of your screw to sit
Here are a couple countersink holes, waiting for a screw to be drilled into
Place screw into hole then then drill it deep into the wood until it penetrates the second piece of wood
These countersunk screws sit just below the surface of the wood…done more for appearance
Here is a side view, the screw heads can’t be seen because of being countersunk