Answer:
'Up, down, to the center, inside' is the literal meaning.
It's a hispanic tradition and it is usually said in the less formal "pa" instead of "para."
While taking a shot of alcohol you raise your glass up and say "pa' arriba," you lower your glass to your hip while saying "pa' abajo," then you raise your glass to your chest to say "pal centro," and then you drink your shot after you say, "pa dentro."