That "Download Fabric API here" link is the gateway for almost every Minecraft player who wants to use mods. Think of it as the "glue" that allows your mods to actually talk to the game and each other.
While the is the engine that runs mods, the Fabric API is a separate library mod that provides the "hooks" necessary for most mods to function. Without it, your game will likely crash or your mods simply won't load. Where to Download It
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