The first thing to remember with this tool is that you must have macros enabled when you first open the file. If you don't, and certain macros aren't allowed to run, it's easy to get out of sync such that when you do enable macros, the spreadsheet is in an invalid state.
Assuming you have had macros enabled since you first started modifying the sheet, here's a brief explanation of each spell page:
- Wizard Spells: This is a list of all spells, organized by level and school. Selecting spells on this tab will place spells in your wizard's spell book (not the Spell Book tab, which is different). Selecting spells on this tab will add rows to the Spell Sheets tab, and will allow you to prepare spells on the Prepared Spells tab.
- Spell Book: The spreadsheet's database of spells. You don't customize your character's sheets with this tab, but you can filter the spells by class/level/school and generate spell cards with brief spell descriptions. Think of this as a reference tab for your own research, similar to d20pfsrd.com's Feats DB.
- Prepared Spells: Just what it says, this page keeps track of which spells you've prepared at the beginning of the day. Selecting spells on this sheet will add little checkmarks to the appropriate spells on the Spell Sheets tab. You only need to use this tab if you have your computer with you on game day.
Spell Sheets: Here is where the stuff you've selected throughout the spreadsheet ultimately shows up. You must select the class for which you want spell sheets in the upper left, and after that you should see the relevant numbers across the top automatically fill in. The area under SPELL LIST should likewise populate with a row for each spell you selected on the Wizard Spells tab and a checkmark for each spell you selected on the Prepared Spells tab.
If one or more of these tabs doesn't seem to be working as described, remember again that you must have macros enabled for the lifetime of the file. If you aren't sure whether macros are enabled, they probably aren't. Check out Enable or disable macros in Office documents for help.