A: Something that is going well / good
B: Liquid being pumped into something to increase its size (Most common use is blood in the muscles after a hard workout)
C: A gnarly wave
A: Hows your day been?
Just swell and yours?
B: Yo brah, im going to the gym to get my swell on, wanna join?
B: Dude, getting punched in the face made my eye swell up like a balloon.
C: Dude, tubular swells out on the north shore today.