In friendly games at home, you might take back a move or fiddle with your pieces. But in a tournament or club game, your hand is your bond. The golden rule is: "If you touch it, you move it."
What if your Knight is crooked and you just want to center it on the square?
If you touch the piece first and then say "adjust," it is too lateβyou have to move it!
If you touch a piece that has absolutely no legal moves (for example, a Knight pinned to your King), you are free to move a different piece. There is no penalty (other than looking a bit indecisive!).
Strictly speaking, no. Online, the move happens when you click or release the mouse. However, "Mouse Slips" (dropping a piece on the wrong square) are final. Most competitive sites do not allow "Takebacks" in rated games.