Second Aid is similar, in most respects, to First Aid.
Where in First Aid you administer medical attention, Second Aid consists of mainly 2 parts.
Second Aid is most often applied when someone, usually (but not limited to) the clumsy or the local blundering idiot, hurts them self.
Jeff: "Oh shit did you see Drew fall down those stairs?"
Scott: "YES! Quickly, let's administer Second Aid before he gets up and hurts himself again."