It should have a world base map, and 100k US topo map. Lake depth charts would be extra. I do not currently own a Garmin but if you go to the settings page and choose maps I think a list will display the maps available on the unit and allow enabling/disabling.
I'm not up to date with lake depth charts, other members will suggest good sources.
Basecamp is the software mapping program for your computer, and managing maps and transfers.
Gps File Depot is a great source for shareware maps.
The Garmin maps are very good but pricey. A
Birdseye Topo subscription looks like a great option. I use a similar subscription from Delorme for the units I currently own.
One of the best map features on the newer Garmin's is the ability to overlay maps and display features of several at the same time.
Sit down with the manual and some spare time. Geocaching is a very good way to learn it's functions.
Have fun with it!
butthead