A workbook is just that, a worksheet is whats in the workbook, kinda like an actual book or a file cabinet. You have the hardcover, and inside you have pages. You can have several worksheets as well to keep related data compiled together. This is a great way for most businesses and personal financing to stay strait. According to www.usd.edu creating formulas for Excel entering formulas into a spreadsheet we want to make as many references as possible to existing data. If we can reference that information we don't have to type it in again. AND more importantly if that OTHER information changes, we DO-NOT have to change the equations.