It depends on what someone has in the way of a "viewer". A RAW (NEF) file is an close to unprocessed data as you can get from the camera, in film terms this is similar to undeveloped but exposed film. The JPG has already been "developed" in the camera, based on the camera settings. In both cases, further processing of the image can be done in programs such as Photoshop. From this you can save to many different formats, JPG is one of the standards that can be viewed by almost everyone.
To process a NEF file you need a converter, such as Nikon Capture NX. You also have more options for processing the data from a RAW file, as it is not reduced to the 8 bits of data in a JPG file.
I would suggest that you do a Google search for Nikon NEF, I will post a couple of links to get you started.
This link from Outback Photo is rather dated but it gives some basics as to "why" NEF rather than JPG or TIF