New to datapacks, interested in worldgen

I want to learn how to mess with worldgen like element X s video on amplified +++++++++ gen, but it might be mods. I'm assuming it's datapacks though, and I'm not sure where to start, I couldn't find any tutorials anywhere. My goal is to create some crazy worldgen like he encountered, layering floating islands, huge lava lakes, and such. It's for a server I'm making. Thank you!