How does Javascript code become asynchronous when using callbacks?

Question

I've been doing a lot of reading online trying to figure out how to write asynchronous JavaScript code. One of the techniques that has come up a lot in my research is to use callbacks. While I understand the process of how to write and execute a callback function, I'm confused why callbacks seem to automagically make the JavaScript execution asynchronous. So, my question is: how does adding in callback functions to my JavaScript code make said code automagically async?