To "get to work" means to begin working. This phrase gives the impression that there is some work that needs to be done, and you need to start on it. You can use it in a command like this:

All right, everyone. Stop socializing and get to work!

Or you can talk about yourself:

There's a lot to do. I'd better get to work.

Of course, these same words can also mean "get to (the place where I) work":

I have to get to work by eight o'clock.