@LottieVixen @bram It's very simple. It's a formal language (so just a toy to build «terms», with no particular «meaning» until you decide to assign one to them) that has expressions of three forms :

«variables» (give yourself a set of acceptable names for variables, just writing the name of a variable is a statement in itself)

«lambda abstractions» λx -> t
where x is chosen in your variables set and t must be a term itself and so recursively can be a variable, or a lambda, or an

«application» a term that you write «f t» where f and t are both terms (recursively again, f and t can be variables, lambdas or applications)