Yes, you need to collect the sap and use that. It's a milky white sort of liquid. A good way is to cut some twigs, make lateral cuts to pierce the outer layers, and soak in water. You don't need to use very much - ficin in a strong enzyme. Something like 4-5 drops of the pure sap will set up a gallon of milk.
It's easier to use leaves if you have them. You can cut the large leaves and drip the sap into a catch vessel.