Beginner Chess Question

Good evening,

I have a question why a certain move seems to be the standard move.

e2e4 e7e5
Ng1f3 Nb8c6
Bf1b5 a7a6
Bb5a4 b7b5
Why is 3. Bf1b5 a standard move? The bishop is chased by the pawns and black is gaining 'momentum' (or is it called 'tempo'?).

Thank you in advance.

It's better to take the knight if a6. It's Ruy Lopez opening. I would take the knight but I never play that opening.

#1
3 Bb5 is a strong move as it brings the bishop into play, prepares to castle O-O and undermines control of Nc6 over the central square d4 so as to prepare a later d4.
Yes, black can chase the bishop with ...a6 and ...b5, but the bishop ends up on the even more active square Bb3, while the weakening with ...a6 and ...b5 can be attacked later e.g. with a4.

#2
4 Bxc6 dxc6 is playable, but not 5 Nxe5 Qd4, but rather 5 O-O, or 5 Nc3, or 5 d4.
Most players prefer to preserve the bishop's pair with the retreat 4 Ba4.

I got this,..

Thanks for the answer

No need to make annotations so long

Instead of stating it’s starting square just say e4 e5 Nf3 Nc6 Bb5 a6 

it’s easier but everyone is special so idk 

You and me both 😂