The Berlin Wall is a very good defense for Black in the Ruy Lopez (Spanish). This tough sideline is played by grandmasters at top level chess events. It was also used in the world chess championship 2014 by Viswanathan Anand.
Black does not play a6 but plays Nf6 instead
1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6
It depends now if White castles or if he protects his e-pawn first. Study all variations to understand how this opening line should be played and get familiar with the various ideas. I selected a video from a chess grandmaster.
GM Leonid Kritz – Being safe with the Berlin Wall Chess Opening
Replay Chess Games with Berlin Wall Defense
Flip Board: Press F-Key (or click e7 or d2 on top) Select a game: Click on grey bar