Let me see if understand. For example you have a 10 page manual. When you go to print the manual you want the 1st page to appear twice on an 8.5x11 inch piece of paper.... each time in a column that is 5.5x8 inches on a piece of paper that is rotated 90º to landscape mode? On the next piece of paper you want the 2nd page of the manual to appear twice in that same column format, etc etc. Is that correct?
First of all... research the two ideas above... they actually seem to know what they are talking about.
However, I have 2 ideas that might also work. Assuming you are working in Pages (other packages will need to adjusted appropriately)
1) Rotate the Letter Sized Paper to landscape. Now create linked text boxes, placed on only the Left (or Right) side of each page. You want to link them so that the text flows from one box into the next - makes future edits and additions much easier. When you are done you will have bunch of pages with text on only one side. When you print, print normally. Then flip the pile of printed pages 90º and print again to put the manual on the other (unprinted) side. Two 'gotchas' to watch out for. One... leave a healthy 'gutter' - that is, the gap between the two columns - so that you can cut without chopping the leading or trailing characters off. Two... make sure that your printer prints first page to last page on one pass, then last page to first page on the other pass to prevent the pages being in reverse order.
2) Better yet.... set up the linked text boxes as above... but then do it again on the 2nd half of the page. That is, you will have two identical sets of linked text boxes on each page. Create the manual in the 1st set of text boxes, then do a Select All, and Paste into the 2nd set of text boxes. Now you can just print normally.
Or - play with the Printer Driver. There are settings in there for "layout" and other things that might help.