I gotta agree with Don that it is cheaper and easier to get a high gloss finish with a spray can over a hand brush. But yes the hand brush can get you a nice high gloss finish, it just wont be otained as quickly.
"Orange peel", which you can also get from a spray can, is when once the gloss airbrushed or sprayed paint dries and cures it has a "pebbly" texture finish that looks like the surface of the skin of an orange. I dont know what causes it, but I have had it happen on a couple builds myself.