A CinePass is equivalent to one ticket. If you have a premium subscription then you will have 3 CinePass each month. Then if you want to watch a movie, you will be given the option "Use CinePass.
If you do not want a subscription or you want to see the new releases outside of your Essential subscription there is also an option to buy a bundle of Cinepass. These bundles consist of a package of 5, 10 and 20 CinePass.