Like all other parents, when he does something properly or well, we applaud him. He enjoys this, and sometimes makes us just sit down and clap while he performs for us.
Most recently, he has discovered another use for clapping. Since he still does not speak, but realizes that clapping makes people feel good, whenever he bumps into me, spills or does something by accident, he claps repeatedly while looking at me with a worried face, as if to say, "I want to make it better." Lately, he claps when I scold him as well, as if to say, "I know I did wrong, it won't happen again." He doesn't stop until I tell him it's okay, and show how we can fix whatever went wrong.
Most cultures use applause to show appreciation. In his own wordless way, my boy does so too. I know he claps to show us that he knows how much we care.