Lesson
White to move. Main line: 1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. Bg5 Be7 5. e3 O-O 6. Nf3 Nbd7
With 2...e6 Black declines the temporary pawn offer and reinforces d5. Both sides develop around the central tension: White pins the f6-knight with Bg5, while Black breaks the pin, castles and supports the center with Nbd7.
White usually chooses between cxd5 followed by a minority attack, or keeping the tension and preparing e4. Black wants ...c5 or ...e5 to free the c8-bishop; solving that bishop is the strategic question of the opening.
The move order prevents common problems. Developing the kingside before moving the c8-bishop keeps the center solid, and White avoids an early cxd5 until the resulting pawn structure matches a clear plan. Study the pawn breaks, not only the first six moves.