Put the screen over the piece so that the design will line up with the background. Since I haven’t printed anything yet, I can see the design through the screen. This is not always the best way to line up your screen with a printed background, but for just one print I think it’s fine.
This is what the screen looks like after you print, before you clean it, which I did immediately, lest the water based ink dry up in the screen and ruin it. (To the left of the Happy Tramps design you can see my Dashiell Hammet egg)