1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 - See King's Indian. 5.f4 - Four Pawns! White claims huge space.
White's plans: Play Nf3, Be2, O-O. Maintain the massive center. Black's plans: Play ...O-O, ...c5, ...Nc6. Break down the center.
Watch the moves to understand the opening sequence. Use the controls to replay or auto-play the variation.