In the world of a map there are four cardinal directions: north, east, south, and west. Similarly, the world of a shield also has four cardinal directions:
Those familiar with Latin or anatomy will notice that, from the viewer's point of view, dexter and sinister are backwards! The usual explanation for this is that directions are specified from the point of view of someone carrying the shield.
In addition, there are four "in-between" directions, analogous to northwest, northeast, southwest, and southeast: