I've seen people who have a flat black truck. Is that just a black primer or is primer and flat black paint? I don't have the money to do much at all with the paint, so I thought I'd just primer it for now and wait to paint. Can any of this come in a spay can?(sorry, I'd love to use a gun, but I don't have one).

probably DP series primer-sealer from PPG. It is an epoxy primer/sealer and water doesnt get thru to the metal underneath, unlike regular red oxide primer. If you have seen these trucks/cars flat black and the paint/primer looks super smooth, its probably because they water sanded with fine grit paper (1500-2000) after spraying. Real popular with the street rod guys and "rat rod" guys.

Hope this helps....

my uncle has flat black primer and a clear over it on his 39 studebaker. looks good