There's a detailed guide on MetaMechs.com on how to use this sheet:
The idea for this is to help Drop Commanders or whoever to make, organize, and communicate drop decks effectively. It's a theory-crafting tool, and I hope some people find it useful.
It may not be necessary for you to go through the whole thing though - for the most part this stuff is decently straight-forward. But there are a few rules which I think are important to keep in mind.
1. You can't edit this sheet, you gotta make your own copy. Do this by going to File > Make a Copy... > name it whatever you want and hit OK.
2. Don't edit the following areas:
Any of the slots underneath the "Tonnage" heading, all the way down to "Special Restrictions" cell (vital to the functioning of the sheet for the most part)
Any of the slots underneath the "Builds" heading, same deal (not as big of a deal, but it's better if you replace the builds that already exist in the "Variants & Builds" tab with the link you want)
I like the titles, but you can change them if you want.
3. Don't copy and paste the cells themselves - double click on the cell to edit it, highlight the text itself, copy, edit another cell, and paste. This retains things like formatting and data validation and other crap which can be annoying to fix.
4. Always keep a backup.
5. Fuck the rules do whatever you want, you can always just copy a new version of this sheet if you break it.