The Queen is the strongest piece on the board. The queen can move diagonally along the color that it stands on and also vertically and horisonally like a rook. Many beginners like to bring out the queen early in the game, because the queen is great at creating different types of double attacks and for eating enemy pawns and pieces. But bringing out the queen early in the game has its risks, because the queen is worth more than any other piece and therefore the opponent can win one or more tempi by threatening your queen. Losing the queen usually means losing the game, while queen sacrifices are considered to be both rare and beautiful.
In the opening, the queen fights for the center or remains more or less passive. In the middlegame, the queen becomes a key piece. The queen is great at attacking, defending and creating pressure. A white queen on Qc2 creates both pressure along the c-file and pressure on the h7-square which becomes critical if black has castled kingside. The queen can create batteries with one or two rooks along files and with a bishop along diagonals. Bc2 and Qd3 is a Q+B battery with the queen in the front. Qc2 and Bd3 is a Q+B battery with the bishop in the front. Qc1 and Rc2 is a Q+R battery with the rook in the front. Generally it is stronger to have the rook(s) in the front.
Q+N is a very dangerous combination for the opponent's king. Together they create many different checkmating options especially if the enemy king is pushed against the edge of the board. K+Q endgames is a special type of endgame with its own rules of thumb and many points can be won and lost in such endgames. Sometimes the queen has to fight against different combinations of light and heavy pieces. Books on this topic are worth while checking out.