At the risk of sounding like a tourist, I'd suggest you take one of the double-decker bus tours to orient yourself to what it all means...uptown, downtown, midtown, Harlem, etc. I know one of the stops where you can buy tickets is across from The Plaza Hotel. I believe it's something like $20 or $25, you get two days to take the tour and it's a hop on-hop off type of thing. After doing that, everything will make so much more sense.

Also, if you're interested in your immigrant ancestors, a visit to Ellis Island is grand. Allow 4-5 hours to look at all the exhibits. You can have a simple lunch there, too.

Have a great time!