how do I make a custom potion? (bedrock edition addons)

How do I make a custom potion with Minecraft addons?
I have seen others do it (at MCPEDL, which is a site that you can most addons, resource packs, and maps).

I don’t want to make a "potion" crafted at a crafting table, which isn’t really a potion, and is counted as a food.