Colin Saint-Vil got his money education at the dim sum cart, over a steamy plate of pork buns and turnip cake. 

A friend offered to pick up the whole tab on her credit card, “for the points.” At the time, six years ago, “for the points” meant nothing to Saint-Vil, now a 30-year-old planning manager in Brooklyn, so he pressed for more details. They lingered over the dim sum meal as a larger conversation unfolded about annual percentage rates, credit-card debt, payment schedules and more.