Red syrups of any flavors you like
but usually Indonesians use either Ros or Cocopandan flavor (shown on picture). Available online and/or at Asian stores.
Cold club soda
Sweetened condensed milk
not evaporated milk.
Pour as much sweetened condensed milk into serving cup as you like (more for creamier and sweeter), follows with the syrup, the measurement is depending on how much milk you added earlier.
Add in some ice cubes, and just before serving, pour in cold club soda.
Stir and enjoy~