There was a question in the Knots SketchUp forum concerning drawing countersunk holes. I decided to do a quick demo showing a way to create them using the Move tool. There are other methods but this is one I find easy. The same basic idea can be used to create chamfers and other details as well.
A llittle while back I demonstrated the Wudworx plugin which has a hole drilling tool to automate this process but if you want to do it manually, this will do it for you.