ELI5: How does the "Live" version of YouTube work?

TL;DR: The "Live" version of YouTube is a thing where you can live stream video and audio to the internet.<br><br>I've never watched a live stream. What happens is there a delay between the person streaming and me watching it? Or is it truly live?<br><br>Edit: If I was to start live streaming myself, would I be able to see a delay between my web cam and what's being streamed? Or would that not make sense?