Chess Opening Theory/1. g4/1...e5/2. d3

1. g4 e5 2. d3
d3 aims to open up the queen side bishop to attack Black's kingside, as well as support a future e4 for control of the center as well. It is basically trying to do two things at once, being hyper-modern as well as classic. Due to this as well as a weak kingside due to the advanced g pawn, White is at a disadvantage, being a jack of all trades, but a master of none.

With good play however, White can establish a mimicry of the King's Indian Attack, with the g pawn able to disrupt the king side knight if it ever comes to f6, meaning Black would have to play h6 to secure it, losing a tempo. Some common moves of this caliber for White include Nf3, Bg2, or the eventual e5, as well as the unique move of g5 common in many games of this opening to prevent Black's knight from moving there.

The main continuation for Black is to play d5, opening up the bishop to attack the g4 pawn, leading to g5. There is also the developing move of Nc6, which defends the e5 pawn and controls d4 along with said pawn.