Can someone explain how Shiny hunting works?

I have my pokeradar and the shiny charms and I have a chain that I'm working on but I have no idea how the odds work and if I have to hatch the egg to know if its a shiny. The wiki felt kinda vague regarding shiny hunting

You have to hatch the egg to know if it’s a shiny. I believe the special rates are hidden to keep people from misunderstanding the statistics and thinking they should have gotten a shiny within 200 eggs if the rate was 1/200, for example. But in general, you have a standard rate of shiny, which you can boost by chaining 39/40+ of the same thing, using charm, and hatching on a Sei day. If I recall, charms boost your odds by 1.5x, and Sei is a bit weird because the effect is higher the less of a boost you have(think diminishing returns if that helps).

I kinda get what you mean with sei - the larger your original odds, the more effect

There is a user-made calculator at this link to help calculate the odds. Please remember that the odds that are calculated are not guaranteed and still depends on the RNG. The Odds are a bit confusing when you try to add in everything but the calculator helps a lot. You can find that link as well in the Trivia section of the Shiny Hunting Wiki Page.