Skip, there are now CPS/USPS and other organizations that teach "GPS navigation". If you are handy with traditional pilotage, chartwork and sextant, this will bring you up to speed on how to work any
GPS, because they all use the same terms, like XTE (crosstrack) and ETA (est. time of arrival). "Programming" them is variable between companies and models, even.
I would suggest you perhaps skip punching buttons on a
GPS entirely, and use it for what it's best at doing: feeding lat/lon coordinates into some sort of PC-based or stand-alone
chartplotter. If you acquire a "puck"-style self-contained
GPS (which are about the size of a stack of five poker chips), you can get various programs that allow you to download the free U.S.
charts and "play" with them in real time. I did this with the SeaClear II program and had fun walking at 2 knots up and down the backyard. I'm lucky I didn't give myself a black eye.
Anyway, because there is no operational standard among plotters or programs, it's doubly important to master the shared concepts they all use. If you go to a boat show and see what the current plotters can do, you can figure out if you want just a 100-dollar
handheld to give you info as basic as a squiggly
line for a track and a little "N" to indicate north, or some five-figure, NASA-like display that gives you a God's-eye view of the harbour entrance complete with live weather, classical music and a reminder that the rum tank is running low.