Noob creating Custom Enchantments for their first data pack ?help?

I've never coded a datapack before but I've done some research so far on structure and the basics. I got the structure down for a "Lifesteal" Enchantment that I'm trying to create but Im having no luck trying to take the damage inflicted by the weapon and turn that into instant health by increments of book level. How do I go about this in the "effects" part? (1.21.2)