The queen is a powerful attacking piece, but it usually needs some help to deliver checkmate. Many basic checkmates use the queen to deliver the checkmate, supported by a minor piece.
The diagram above shows a queen and a knight working together to checkmate a king. White can finish the job by playing Qe7++.
Although this example is simplified, it illustrates an important checkmate pattern that can be utilized with the queen along with a supporting piece. Against a king stuck along one of the board's edges, a queen -- supported by another piece -- placed directly in front of that king will always deliver checkmate, provided it cannot be captured by a piece other than the king.
This pattern works because the queen takes away every square the king might flee to. For example, in the diagram above, a White queen on e7 attacks d8, e8, f8, d7 and f7, meaning the Black king has nowhere to run. There are no squares between the queen and the king, so there is no chance to block the check. The queen is supported by a knight, meaning the king cannot capture the queen. Black has no other pieces that can capture the queen either; with no way to avoid capture, Black's king is checkmated.
