Using drag and drop to move a piece is not difficult.
You simply click the mouse on the piece you want to move, then move the mouse until the selected piece is over the target square, then release the mouse to drop the piece onto the target square - and the move is done!
For example, let's say you want to move your knight to a different square.
Move the mouse over the knight, click and hold down the left-mouse button, then move the mouse. You will see that the knight also moves as you move the mouse around.
It is not possible to select any piece which you are not allowed to move, for example, a piece belonging to your opponent. You can click on the piece but the mouse pointer changes appearance to indicate that the chosen piece cannot be moved. Just release the mouse button and try moving a different piece.
Once you start to move the knight, you will see that all the squares to which you can move the piece are highlighted. You can move the knight to any one of these highlighted squares.
In the diagram, you have a choice of two different target squares to which you can move the selected knight. Or you can return the knight to its original square which is also highlighted; this cancels the move and allows you to start again, or to choose a different piece.
You can also cancel the move by simply moving the knight over any square that is not highlighted and releasing the mouse; the knight will return automatically to its original square.
You can also hit the Esc button on the keyboard to cancel a move and the piece is instantly placed back on its original square.
It is not possible to move a piece off the board!