When you need to supply your artwork in pagination or printers pairs. The most simple way to work these out is to make a mock up of your intended booklet using blank paper and simply write the numbers on the pages. Start with Page 1 being the front cover and then continue numbering until the last page or back cover is the last number. Nearly all booklets are constructed out of 4 pages, or multiples of 4 pages.
For example, a four page booklet is one piece of paper folded in half, the outside pages when viewed as a flat sheet would have Page one is the front cover, Page 2 is the inside left hand page, Page 3 is the inside right hand page, and Page 4 is the back cover or last page.
Please refer to the example below.

You’ll see I have worked out an 8 page and a 12 page booklet for you, you can work out bigger booklets Eg: 16 page, 20 page etc by simply doing as I suggest and make one up with blank paper and write the page numbers on, lay the sheets flat to see your printers pairs.