In this case, page does not mean a sheet of paper. A 100 page book has 100 pages and 50 sheets of paper. Books are printed in minimum units of 8 pages so round off your page count so that it is divisible by 8. This is the finished size of your book. However, we can print any size.
Most books bind on the long side.
In other words, a book that is 6 x 9 is 6 inches across and 9 inches tall binds on the 9 inch side. A half tone is a photograph. Photographs should be supplied to us exactly the size you want printed and placed on the page. Should be supplied exact size and placed on the page. Margins are the blank paper between the text and the edge of the page.