https://datahubproject.io/docs/generated/metamodel/entities/mlfeature, It has schema defined here, what is the use of these schemas ? Can we use these schemas to make aspects ( like we do by using a .pdl file ) or Is it just for understanding purposes?

I believe this is just for understanding, you’d need to extend the metadata model to introduce new aspects https://datahubproject.io/docs/metadata-modeling/extending-the-metadata-model