I suspect you now have only a single page to your file.

To add a page, select Insert, Page.

Create the second page.

If you don't have a duplex printer then print page 1 of 1;
put the paper back into the paper tray and print page 2 of 2.

You need a printer that has duplex printing. My Canon pixma ip6000D does.
 Otherwise you have to print one side, and turn the paper over, put it back
in and print the other.
If this is what you mean?
 You say print double sided and not "set up" (in Publisher)