According to this, it's a GPS watch that records exercise activities and heart rate and has sleep monitoring and other such features, and connects to a phone for analysis of the recorded stats: https://www.dcrainmaker.com/2015/01/fitbit-surge-depth-review.html
That article specifically says that you cannot load maps, routes, nor waypoints, and therefore is not suitable for Geocaching. You'll need other ways than a Fitbit Surge to locate a cache. But you can monitor your fitness while you do.
Thanks so much - just the information an average middle aged technophobe needed!