Connected Passed Pawns
Two passed pawns side by side, connected passed pawns, are the most powerful pawn formation in chess. They protect each other as they advance, and a piece can only stop one at a time. On the 6th rank, connected passed pawns defeat a rook. On the 7th, they're nearly unstoppable.
Why they're so strong
Connected passed pawns protect each other, if one is captured, the other promotes. A piece trying to stop them must choose which pawn to blockade, leaving the other free to advance. On the 6th rank, two connected passed pawns are worth a rook. This is a fundamental endgame rule.
Creating connected passers
The most common method: exchange pawns on adjacent files to create two connected passed pawns. A minority attack can also create them. In rook endgames, trading rooks when you have connected passers is often decisive.
Training
Study positions with connected passed pawns in the legends database. Practise advancing them against the computer.