Can’t Remember Selection Shortcuts? Look At The Cursor
If you've made a selection and want to add to that selection, just hold the Shift key and you can add more area to it. Of course, we just told you it was the Shift key, but what if you couldn't remember which key it was? Just press a modifier key (such as Shift, Option/Alt, Command/Control, etc.) then look at your cursor. When you hold the Shift key, a little plus sign appears at the bottom right-hand corner of the cursor to tell you that you can add to the selection. Hold Option (PC: Alt) and a minus sign appears to tell you that you can subtract from the selection. Hold Command (PC: Control) and a pair of scissors appears, telling you that if you click-and-drag the selection, it will cut out the image inside of the selection and move it right along with the cursor.