Countersinking is a technique used when drilling a hole into wood. The goal is to create a small depression around the circumference of the hole so that the head of a screw can be flush with, or slightly below, the surface of the wood. This ensures a strong connection and prevents the screw from working its way out over time.
There are two main ways to countersink on wood: by hand or using a power drill. When doing it by hand, you will need to start with a pilot hole that's slightly smaller in diameter than the screw you're using. Drill this pilot hole to your desired depth using a standard drill bit. Next, switch to a countersink bit - these have an angled tip that will create the necessary depression around the hole as you drill. Slowly lower this bit into the pilot hole until it reaches your desired depth and then begin drilling. You may find it helpful to go slowly at first until you get a feel for how deep you need to go - once you've reached your target depth, finish up by drilling out any remaining material until your countersink is complete.
If you're using a power drill, things are pretty similar except that you'll be starting with either a larger pilot hole or no pilot hole at all (depending on what size countersink bit you're using). Begin by attaching your chosen countersink bit to your drill - make sure it's secured tightly so that it doesn't slip during use. With the drill turned off, slowly lower the bit into place over your pilot hole (or mark) and then turn on the drill - start slow and then increase speed as needed until you reach your target depth. Finish up by backing out of the holes once you're done drilling; this will help prevent any chips from getting stuck inside of your newly-created countersinks!