Entitlements regulate what out-of-process facilities you're allowed to access. (For example, entitlements let you access certain parts of the filesystem, or the network, or access location services.) Private APIs are regular boring in-process classes, methods, and functions which just aren't documented by Apple and aren't part of their public interface. You call them in the same way as you do a public API: by jumping to the function, or invoking objc_msgSend to send a message to an object, all within your process.