Black prepares e7-e5 as well.
1. g1f3  1... d7d5  2. g2g3  2... g7g6  3. d2d4  3... g8f6  4. f1g2  4... f8g7  5. e1g1  5... e8g8  6. a2a4 White has all sorts of moves in this position to avoid the main theory of 6.c4—this is just the eleventh most popular move, to give you an idea. The intention is to gain space on the queenside with a4-a5, but I understand that this is a bit vague. 6... a7a5 A natural move, preventing White's plan that could go ahead against 6...c6 or 6...Bf5, not that it's anything too impressive. 7. c2c3  7... c7c6  8. b1d2 Now White wants to play Re1 and then e2-e4, getting a nice pawn structure. 8... b8d7  9. f1e1 