What does it mean to countersink a screw?

to counter sink the screw means the screw head should lay under the wood surface-- the head should not stick up past the surface of the wood

to do this I use my drill with a Phillips head bit and bore a hole in the wood while swirling my wrist and pushing down to widen the hole a bit-- this makes the head hole a bit larger and allows the screw head to sink below the wood surface without creating any wood splintering around the top of the hole by over forcing the screw