Padlock keeps your view centered on the plane you are currently targeting. To select your target, hit TAB (?), then hit the padlock key and you will be looking at that plane no matter where you are pointing or pressing other view keys.
There are also selections for snap view and pan view, that is, snap view looks to your nine o'clock when you press the 4 keypad key, pan view will pan your view slowly around leftwards when you press 4.
Hope these help.