Hey Spy
This is the Garmin page for the 276C
http://www.garmin.com/products/gpsmap276c/And this is the page for the newer model, the 376C (cost more and more options)
http://www.garmin.com/products/gpsmap376c/As far the operation. When it is in the "street mode" it works probably like most of the other typical GPS units. Shows you the detailed maps, and a variety of other "places" like fuel (have used that feature more then once), lodging etc. And you can look up addresses.
The driving directions are pretty good too.
When you switch to "marine mode" it acts just like a plotter with detailed charts.
Like I said before, I switch it back and forth between my truck, the bike, my whaler and any other vehicle I get in or boat I my drive. Heck, I even had it in the window of a 777 coming back from Vegas in February, that was cool. You can see pics of it on my whaler here
http://www.porthole2.com/porthole/photos_Whaler_3.htmThe plotter functions just like any of the other bigger plotters, just remember you are using a small screen. It has all the typical plot and navigate functions along with all the alarms.
The sounder requires a "black box" option. You can see that mounted under the whaler console here.
http://www.porthole2.com/porthole/photos_Whaler_4.htmThe transducer options are all the same, transom mount, through plastic or bronze etc. Actually, the black box is compatible with most Garmin plotters.
When the sounder is active (sorry no pictures, but I could snap a "demo mode" pic if you like), the screen switches to a "color video" mode, which can also be split with the chart. It works pretty good for what it is. I don't think I would use it as my primary on my big boat, as the unit is compact, but I don't hesitate to take it with me on the big boat. The sounder works just like any other color video sounder would.
All in all, when in either the chart plotter or Street mod the unit functions just like a dedicated unit.
Hope this helps.