The rules are simple gambling rules
As for the spread sheet,there are a ton of websites that offer spreads for games,I refer to bookmaker.com and pinnaclesports.com for my lines that I use
The easiest way to explain how it works so there is no confusion going forward:
Any team that is -x has to win that game by more than x
Any team that is +x either has to win the game,OR lose by less than x
Minnesota -4 over Green Bay
If Minnesota wins by 4
OR
If Green Bay loses by 4
It's a push(tie) and there is no winner
If you bet Minnesota,they have to win the game by MORE than 4 points
If you bet Green Bay, they can either win the game outright, OR lose by less than 4 points