They give you credit for 1 per cent of your purchases. Go to the Customer service desk and present your card and whatever document you used to open the card account. They will issue you a paper looking like a cash register receipt. Pass it to the casheir when checking out. End of March is presumably the date each year when last year's expire.
Actually, you get 1 point for each 100 pesos spent.
If your purchase comes to 499.99 - you get 4 points, not 5.
That part always annoys me, I pay 500, but only get 4 points (20% point rip off).
.. and on top of that they have no problem ripping you off for a peso or two in change.
They have not quite master the point system yet, you actually earn points on the points you cash in, same ratio, you earn 1 point for each 100 points cashed. (Or combination cash/credit/points)