Custom Weapon Help

Hello, I am extremely new to datapacks, I've made custom resource packs before and I am currently making a datapack to add custom abilities to these weapons. I've followed multiple tutorials and such and I just cannot figure out to to even add particles to the entity I am hitting. 
I cannot figure out how to link the custom sword to a mcfunction and if I cannot simply add particles, then I will be unable to do things such a teleportation or random potion effects. I have custom model data of 2070001, but I do not understand if that is used to link a function to another one, or how the game checks to see if I am holding that specific weapon, I am at a lost. :(
I am on version 1.21, I have updated all the directory names I believe, and I can even link the datapack if someone would like to take a look at it.
I can link or show anything else if needed, any help would be greatly appriciated.