CTL+INS places a reference point. CTL+DEL deletes a reference point. CTL+R renames a selected reference point. CTL+END de-selects all references points.
Reference points can be made relative to a unit. For example you can create a set of reference points that will follow a carrier. You can also make the reference points so they rotate depending on the heading of the unit. This is particularly useful for setting an anti-submarine warfare patrol mission in front of a carrier group.
CTL-Right Click and select either Define Area - Rectangle or Define Area - Circle. Then click and drag to create a set of reference points. The circular reference point area is particularly useful for setting a patrol area around surface ships.