Hello, I'm new to modding I just started a Java course and I wanted to put into practice what little I learned by creating a simple Minecraft mod. I didn't think creating a mod required all this Java knowledge (which I don't have) so I followed various tutorials on how to set up the workspace and to create the bases that is a custom block, a custom item and how to make the block spawn in the world. Now I would like to make the block spawn in the world more infrequently and in 1 block veins. To do this I realized that I should use "Feature.EMERALD_ORE" and "ReplaceBlockConfig" instead of "Feature.ORE" and "oreFeatureConfig". Unfortunately I couldn't find any tutorial or examples on how to use the emerald feature, I've also tried to look at how mojang adds it to minecraft and I didn't figure out how to adapt it to my mod.
Any help is welcome, if you have any examples to show me I would be super grateful and in case you want to take a look at my code I'm pushing everything I do on my github
https://github.com/TYPyz/dNode

first of all there are a lot of threads with these topic, just search in the Forge
second you can take a look at the vanilla Ore generation, OreFeatures and OrePlacements are the classes you should look at
note that you need to register the Features and Placements in FMLCommonSetupEvent and add them via BiomeLoadingEvent

How do I register Features and Placements? 

via FeatureUtils.register and PlacementUtils.register