A paste-up (some call it a mock-up) is a way of organizing your items on one page, arranging them how you want them to look on the final draft, making sure everything fits and the "flow" of the page makes sense.

Newspapers do paste-ups of their pages. I used to work on a few papers when they still did things by hand...but now things are done mostly on the computer. It's still called a paste-up, though.