You can do this using a relative position and place referenced to that, or you can place using the Type Offset or Type Coordinate commands from the context menu.

To change the relative origin, select the reference item (a pad for example), and from the context menu, select Origins and Set Relative Origin At Item.

The status bar will change to display Rel (instead of Abs), this indicates that you are in Relative coordinate mode.

All movement and pad positions will now be relative to this position.