I am having a hard time understanding lambda expressions in Kotlin...

they're a way to pass behaviour, instead of data.

A lambda is just an easy way to send a function to someone

Are you familiar with higher-order functions? If not, maybe this should be the place were you start -> https://kotlinlang.org/docs/lambdas.html

lambda expressions are anonymous functions (they have no name) that you can manipulate just like other data types, eg: pass them to arguments, return them as values, assign them to variables. An expression like

(Int) -> Boolean

IS the type of a lambda, just like

Int

, meaning a function that takes an Int argument and returns a Boolean value.