how do i set alarm on scenic 1.9d 2005?

i've just bought a Renault Scenic 1.9d 2005 & i've got keyless card with 3 buttons on, (not sure which button is which to start with!!) When i think i've locked the car there's a buzzing sound but when i try the handle the door opens, so the car's not locked. The gargage owner is getting me a manual, but obviously i need to know how to lock the car now. Anyone able to help ???

tony
December 2008