How does YouTube monetization work?

I just hit 500 subs today, I have 528 subs now, and I have around 4.5K watch hours on long form content. I know I can’t earn Adsense till 1K subs but I was more or less wondering how the application process works, or how long it takes? When I hit 1K subs do I need to apply again?

You don’t gotta answer any of the questions, I’m just looking for anything related to it lol