It was a bit confusing to me too. Go to the file manager and select an stl or print file, or upload an stl file. Choose PRINT NOW (a bit confusion why they didn't add another option like "Print Later" in that popup or change the wording to just Print). It will then present you with two options, Print Later, and Add to Queue. I am still not sure what Add to Queue does, but Print Later adds the file to the Queue. There is also a number and arrows to increase or decrease that number next to the Add to Queue button, but I also can't figure out what that does either. Switch to your Print Queue screen and you should see your job in the Queue now.