Reflection maps are spherical images that are applied to material as, well a reflection map, so that the material has something to reflect to the viewer so it looks like its in an environment.

The kind of effect that they have can be seen in HDR rendered images (althought HDR images are mainly used for some sort of lighting) the JD bottle I did has a HDR on it that provides the relfections, as well as some of the cars that people have done.

For learning the fields just create an emmiter and add each field and play with the magnatudes and other settings to get a feel of them.

Cheers