Some beginning players have a tendency to pick up a piece and then start to move this piece over the board searching for a good location. They seem to think with their hands.
Try to think before you move. Do the moves in your head. This will help you to visualize the board and also enables you to think about what your opponent will do after your move.
Even more important the touch-move rule in chess forces you to move or capture a piece you have touched during your turn. Please note the capture part in this rule. If you touch a piece of your opponent you have to capture that piece.

If you are moving a piece the move isn't completed as long as you haven't released this piece. You are even allowed to move a piece in a completely different direction as long as it is a legal move. As soon as you have released the piece the move is considered to be completed and you are not allowed to change your mind. This rules sometimes causes that players are almost afraid to release their pieces. Try to avoid this. Think before you move. Most blunders are made by players that change their mind during the short time frame of the actual move after a rather good evaluation of all the consequences of their intended move.

Summarizing these official rules a piece that has been touched has to be moved. A move is completed as soon as the piece has been released and may not been taken back.