The most important rule about passed pawns to know is that two connected passed pawns, if you can get them to the sixth rank, are worth seven points. It’s as if suddenly an extra rook appeared on the board for you, if you can get them there. It can be worth a piece sacrifice to get them there, and you will suddenly find your opponent willing to do just about anything to get rid of them, including sacrificing his own pieces. If you have a pawn majority, meaning you have one more pawn than your opponent, then, so long as they are not doubled, you can create a passed pawn if they are pushed far enough up the board (ie. especially the sixth rank). Because then if you have to sacrifice a pawn to get your opponent’s pawn out of the way, you get to queen your pawn. And since you’re closer to the eighth rank, you queen first. So even if your opponent gets a passer, he won’t be able to queen it. For a very instructive game about pawns on the sixth, take a look at Grigory Serper vs Ioannis Nikolaidis 1993 St. Petersburg Open.