Pssht is a greeting.
All you have to do is stick out your thumb, index, and pinky fingers and say, "Pssht!" whenever you see your
friends.
You can do a behind-the-back pssht or an under-the-leg pssht, etc.
You can say it really long,
like "Pssssssssshhhhhhht," usually by adding more
s's and h's.
The pssht is kind of
like Spiderman -- oh wait, except NOT! Notice how Spiderman doesn't use his thumbs, his webs come out of his wrist not his fingers, AND he doesn't say "Pssht."