Choose the number of pages your brochure will have and how its folded.
For example, a single A4 sheet folded in 2 would be a 4pp 1 fold. 4pp meaning 4 pages (front, inside front, inside back, and back page) and 1 fold meaning there is only one fold in the sheet. A roll folded DL would be a 6pp 2 fold (1 A4 sheet folded 2 times with 6 individual pages).
Expample of 4pp 1 Fold
Example of 6pp 2 Fold