1. Tabs are at the bottom your Excel workbook, they help you label each worksheet in the workbook as a whole. When you open a new spreadsheet, there will be only one tab at the bottom–click on the + sign to add a Worksheet. Double click to change the name. Right-Click (Or Control-Click) to get colour options.
2. The formula builder will help you calculate the different items being asked for in the assignment. Or, you can usually type in the formula: =sum(A1:A8). For subtraction, you can use the formula =sum(A1-A8). You just need to put in a subtraction sign!