get down to (doing something)
To begin doing something with the seriousness or determination the action requires; to begin doing what needs to be done. OK, let's quit fooling around and get down to work. I guess I better get down to reading before I'm too tired.
get down to (doing) something
to begin doing some kind of work in earnest. I have to get down to my typing. John, you get in here this minute and get down to that homework!