Scotch Game is a chess opening with the ECO code C44. It goes 1. e4 e5 2. Nf3 Nc6 3. d4 exd4. White opens with 1. e4 (the king's pawn) and Black answers 1... e5. After 6 moves it is White to move. After the last move Black is a pawn ahead in material. The lesson on the board explains every move of the line and lets you play it yourself; it is free.
In chessGM's opening book this position continues with 4. Nxd4, 4. Bc4.
After 1.e4 e5 2.Nf3 Nc6, White plays 3.d4 at once to open the centre. It leads to open, clear positions with fast development.
chessGM has a full course for this line: open the Scotch Game course lesson.