The ticket is bought at the sports centre counter probably at the ground floor. When u enter the gym, just pass the ticket to the person at the gym's counter (it's somewhere near the door, won't miss it. The people manning the desk would be probably instructors in blue clubfitt instructors' uniform).
Regarding lockers, there are 2 sizes, 20cents and 40 cents.
This applies to all clubfitt gyms in Singapore.