Custom Potion Drops 1.21.4

Hello! I've never made a datapack before but I've run into a wall with what I know how to do with command blocks. I frankly have no idea where to start, but heres what I need help doing: I have a vague understanding of file structures However I've no idea how to do what I want to. I just need to add a loot table to the game that will spawn a custom potion (swiftness, nausea, darkness) I know how to manually apply loot tables IN game, so I just need some help figuring out how to get the loot table in the first place any help is appreciated! My version is Java 1.21.4