One Sheet = Two Pages
A single sheet of paper has two sides. Each side is considered one page even if the back side is left blank. So a sheet of paper is always two pages.
One Sheet Folded = Four Pages
A sheet folded in half becomes a four page document. Page one is the outside front cover (OFC), page two is the inside front cover(IFC), page three is the inside back cover (IBC), and page four is the outside back cover (OBC).
Two Folded Sheets = Eight Pages
Two folded sheets that are nested together are counted as an eight page document.