If you only have 2 wheel drive do you still need all 4 tires or can you get away with just the 2 on the drive wheels?
For the most part, buy 4. Otherwise you'll be choosing turning vs. moving unless you're driving a fwd. Also, see below . . .
And is this something I was supposed to have?
This will be my third winter up north. I heard someone talking about Winter Tires and I was completely nonplussed. Have I just been lucky I haven't died yet? Is this something everyone knows about and has?
What kind of car do you have and where do you live?
I have a Ford Mustang 6 speed manual and I live outside of Philly.
In general, if you have to ask then you're not messing with /modifying your car and it probably came with all-season tires and you'll be ok. Unless you bought it somewhere that was warm all year, but even then, I think it's cheaper for car manufacturers to go with all season tires anyway.
Still, as a RWD performance car, you'll find winter tires far more manageable in snow/ice, especially if you have no experience driving in winter conditions.