Part 23 is on page 8 of the plan's and part 23 is on page 9. You glue both part's 23 and 23 together to make one larger piece and glue part's 24 and 24 together as well. Like on page 7 of the instruction's.
Once you got those glued i believe they are glued together to make a even bigger piece. Hope this help's
Post some picture's when you can.