• Simplex refers to printing on only one side of the paper.
• Duplex refers to printing on both sides of the paper.
• Not all printers have a duplex attachment. To print duplex on a machine without the attachment, print one side of the paper and then re-insert the sheet back into the printer manually so that the other side may be printed. A duplex attachment speeds up the duplex process considerably and reduces errors.

You will see options in print settings for short-edge or long-edge. If you don't know which option you want, print two pages of the document you want in duplex mode. Then verify both sides of the sheet of paper to see if it was done correctly.