kwitel

Hey all,
So i really know squat about bikes...
Im looking for something I can ride in New York City and potentially take offroad.
I thought I was going to buy a Dual Suspension-but that apparently is out because they are too slow on the street?

So, Im trying to understand the difference between a Hybrid and Hardtail (if there is one).
Also, I have a minimal amount of money to spend and have NO CLUE where to start (<$300)

Lastly, are things like an aluminum frame or disc brakes really relevant for me?
Thsi will be predominantly recreational riding in Central Park and some offroad for fun; trying to guage what level quality bike I NEED to start with.

Any help/advice you can give is greatly appreciated.

Thanx!