I'm not going to write a lot of background here because reems have been written elsewhere, and some of it better than I would have done. So I'm mainly going to limit it to what I know about mine.
This is a Nikon F Photomic FTn. The F is the actual body style, which was made for 15 years by Nikon and was largely the same throughout its run. The Photomic FTn part describes the viewfinder.
The major differences in the F series are in the finders. The original F had the pentaprism that we all know and love, but it had no on-camera exposure meter. Nikon had made the finder detachable, so you could buy the Photomic finder that had a CdS cell mounted on it. They later improved it with the Photomic T, which moved the cell inside and measured the light through-the-lens (TTL). They later updated it again, and called it the Photomic FTn. This one added some extra features and is generally regarded as the best of the lot.
According to McBroom's Camera Guide, a source I trust, the serial number series for Nikon Fs begins with 6400001 and goes upward (remember that this would be in 1959). By the mid-to-late 1960s, the first two digits coincided with the year of manufacture, and at some point, Nikon set things up so that the first two digits really did correspond to the year. Even if it's not dead-on accurate, it will give you an idea of where your Nikon F fits in the timeline.
Mine's a 1974 model, which makes it one of the last ones made. Again, according to McBroom, these were usually more valuable simply because they were younger and would likely reflect less use. Of course, my McBroom book came out 1995 when "young" Nikon Fs were only 20 years old, whereas now they're in their 40s.