When does a web page appear the first time?

I'd like to know when does a web page appear the first time, especially in relation with events like the DOMContentLoaded or or the Load event.

If I knew the event in question then I could minimize the HTTP requests up until that point and lazy-load resources after that. My knowledge on the subject is admittedly limited and I know that it's a very broad topic but I'd rather like some practical info.