Here is an explenation to all stdlib function and how they work in lambda calculus.
Read wikipedia page on lambda calculus and watch some videos.
Natural numbers are represented by a function that takes 2 arguments, a function and some value. It then applies function to the value n number of times.
True is a function that takes 2 argument and returns 1st one. False is the same but returns 2nd argument.
Always and Never functions can be usefull sometimes, they are self explanatory.