The answer to this is Command + T, cmd + T, apple + T, command and T, command+T, Control + T. Do remember that before doing a command, it is best that you already know the item that you are going to transform. This will allow you to make different transformations in a free manner. A lot of people love doing this because of the freedom that they receive while making the necessary changes.
It can be fun to use but make sure that you do not go overboard. A lot of people are adamant about protests made with the excessive use of Photoshop. Try to keep things as natural as possible and you will do all right.