I've demonstrated what the counter-sink does on this tool right here. It makes a hole so that the screw goes down there and you don't see it and it makes a nice round hole for a plug. Now you have several options on doing this. You can make your counter-sink, put the screw in and just leave it alone. That looks okay in a utility setting and sometimes maybe even for cosmetics it' kind of interesting look. And that's what that looks like. Another option is to put the screw in like this and simply put some of the filler in the hole. The same filler we used on the cracks in the boards you can just fill the hole up with it. And that's what it looks like. That's really good for painting and it also stains pretty well. A third option is to put a plug in the hole. And we're going to do that later in our bookcase. Just a small plug will go in that hole. That's a really nice way to make it look. Another option is to just drive the screw in with no counter-sink at all. That's what that looks like. It gives you kind of an ugly hole. The other problem is that you can't take this screw out once it's driven in because the wood fibers have not closed over the back of the screw. If you're going to paint the bookcase, this is an okay way to do it. And then after you drive that screw in, we'll just fill it like that and later we'll sand it out. We're going to put our bookcase together now but I'm going to use the plug method and we're going to put plugs in, and our bookcase is going to look pretty much like that after, before we sand it off. So, we'll get on to that here in just a second.