Does anyone know exactly how the point systems work for the POSB Passion Debit Card?

It's the TapforMore Rewards Programme. In participating merchants (coldstorage, guardian, jasons, giant...), $1 spent gives you 1 point. 150 points can help offset $1 (about 0.67% rebate). You can earn free points by attending grassroots events. Members can also enjoy other benefits and privileges such as exclusive offers and invitations to special events/activities.