The PRT SCR button would actually print the screen on old DOS machines. Now it copys the screen bitmap into the clipboard. If you then paste the clipboard into a paint/photo type program, you can edit/print it from there.
Well on my computer if I hit shift prt scr and then open an application like Wordpad and then right click / paste, a copy of my desk top gets pasted into the document. You can then select print from the application if you want a hard copy.
So the fundemental thing is that prt scr places a screen shot into the windows clip board, not directly to the printer.