How to Reverse Engineering a Phone App

Dan: There's two reasons why people are reverse engineering. One is because they want to see what's going on, right? They understand all the steps that are happening. And then the other one, Dan, as you mentioned, is to replay and do it programmatically,. Do it super fast. Is Charles proxy something like that? Or is it what is Charles proxy or do you know of tools for being able to understand how phone apps are working?