We highly recommend our Figma plugin to create an avatar style. Most of DiceBear official avatar styles were created with the plugin. But with appropriate programming skills you can also create an avatar style without Figma.
As you can see, it doesn't take much to create an avatar style. Both the metadata and the JSON schema are optional. The create method takes the PRNG and options and creates the avatar. What you do exactly in this function is up to you.
If you specify metadata, it will be placed in the metadata of the created avatars. If none are specified, the avatar's metadata is empty accordingly.
The JSON Schema object describes the allowed options that can be passed to the createAvatar option. It is mainly used by the CLI, the API and the documentation. So you can leave the object empty without any real disadvantages. But it can help to document your avatar style.