What is the difference between an Oracle schema, user and authdomain?

In Oracle database we don't have any difference between schema and user both are the same. Each user = schema can have their own objects based on the grants given by Dba to the user

I can say for sure that if you work a lot with Oracle schemas, then you will need a comparison and synchronization tool. What I like the most is the dbForge universal tool, as it can be used for oracle set schema and oracle schema compare. And also it will be a good helper if you need to make big changes to the database and analyze their impact.