a Point/ a Vector
To use a Point, you may not need to create a reference point if there is already some location (element end point, center, etc.).
To use a Vector, you will be prompted to indicate two locations. Again, you may or may not need to create reference geometry, depending on the elements available in the drawing.
Usually a line is good to use as a reference vector.
The location of the surface corner with the arrow is used to determine which side the arrow should point toward. For complicated geometry, you may need to do the alignment in more than one step.