You shouldn't take someone's tip money because that's stealing.
Marty is a busboy, and he and the waitress Ann are the last ones in the cafe when it's time to close.
Marty needs to clear the last table before they leave.
Marty sees Ann's tip money is still on the table when he's clearing it, and he brings it to her.
When Marty goes to clear the table he sees a customer left Ann a tip, and he pockets the money for himself.
Ann thanks Marty and tells him she forgot all about her tip.
Ann sees Marty put the tip money in his pocket and asks him what he's doing taking her tip money.