The idea is that it's a set of basic rules that can be used to model any computation (lambda calculus is Turing-complete). So think of it as a programming langu

The idea is that it's a set of basic rules that can be used to model any computation (lambda calculus is Turing-complete). So think of it as a programming language with a very minimal set of primitive/builtin operations, which is really what it is. The reason things can seem more complicated than they need to be is that this set of primitive operations is so minimal; and the reason it's so minimal is that Alonzo Church came up with it in the 1930s when they were trying to get to the very bare bones of the concept of computation. Lambda calculus is the grandfather of all functional programming languages. Lisp was a more or less direct implementation of it