Instructions
White opens by moving the king's pawn to e4. There are a number of strong points to this move. White can begin to control the center of the board, and White's queen and bishop are now free to be brought into play.
Black responds by mirroring with e5. This basically gives Black the same advantages that White has.
White moves a knight, Nf3. This brings a piece into play, strengthens control of the center of the board, and attacks the pawn on e5.
Black counters by also moving a knight out, with Nc6. The knight is now defending e5 while improving Black's own position on the board.
Now White moves the bishop, Bb5. This brings another piece into play, opens up White's ability to castle, attacks the knight, and can potentially lead to a pin position.