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.

If White wants to open up the center, what should White play?

White opens up the e-file by trading pawns. It's not the most exciting opening, but both sides should focus on piece activity and being ready to fight for open lines.