IngeniousCoders

I am trying to create a custom entity in minecraft, but I have searched as much as I could around the internet and everything is confusing and nothing works. I was wondering if someone could just break down what one needs to make an entity in simple form from the ground up. Please help and Thank you in advance.

I am trying to add a custom fluid to minecraft in 1.17.1 I need some help and I have asked and searched as many places I could for help on this topic. I made the classes and properties for the fluids but I can't add them to a tag.