Ruy Lopez with 3...Bb4 (Alapin) (game 114)
Main idea: after 3...Bb4, use c3 and a4 to kick the bishop, then trade on c6 and take the pawn on e5. Black's queenside pawn structure becomes weak while White keeps a lead in development.
Opening moves: 1. e4 e5 2. Nf3 Nc6 3. Bb5 Bb4. This is the Alapin variation. Black stops d4 for the moment and plans ...Nge7, but allows White to gain tempi by chasing the bishop.
White uses c3 and a4 to attack the bishop, then plays Bxc6 and Nxe5 to win the centre pawn and keep the initiative. This page follows the 1.e4 repertoire PGN (game 114) and explains the ideas in simple language.
Main idea: after 3...Bb4, use c3 and a4 to kick the bishop, then trade on c6 and take the pawn on e5. Black's queenside pawn structure becomes weak while White keeps a lead in development.