See: How can I help?
Good question.
Simply put, all you have to do is flip over your paper. The problem is, how do you orient the piece of paper after the first side has been printed so that
nothing messes up (i.e. the second side is upside down)? The following diagrams should help.
1. Printers that feed from the bottom (or from inside a tray).
The 'A' side is the side with stuff on it already. the side that cannot be seen is the blank side.. the side that is going to be printed.
2. Printers that feed from the top.
You might mess up printing double sided if you're unfamiliar with it, but after one or two tries, it'll be second nature to you.
So what do you do if you're printing multiple pages (say, 10)? Well, first, you want to print the even numbered pages.
Then, pick up the 5 sheets of paper (or however many you have). Flip the whole stack over, and put it in the printer again with the
orientation above. Then, print the odd-numbered pages and you should be left with 5 sheets of double sided sheets of information, and not 10!