Open, closed, and semi-open games

There are three main categories of positions. If there are few pawns on the board the position is open. Bishops are often very strong in these positions because they are not blocked. If there are many pawns blocking each other on the board, the position is considered closed. Bishops are restricted by the pawns in these positions, so knights are the dominant minor piece. Many positions have some features of open and closed positions, and are considered semi-open.

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White has sacrificed a pawn for a lead in development and opened up some lines to attack. How can White develop a rook to a semi-open file and create a dangerous threat?

Black makes a careless move, not realizing that White wants to open up lines for attack. How can White open up the center and regain the sacrificed pawn?

Black tries to add pressure to the e5 pawn, but what should White play now?

White opens up the queen on the e-file and regains the sacrificed pawn. Black cannot recapture the pawn because Ne4 will win the bishop, so White has a great position.