Actually, Oracle automatically creates a schema when you create a user , the schema name is your user name. All tables, views, indexes and privileges created by this user will belong to this schema.
And if you don't specify, all those objects will be created on default tablespace of this user
Schema's difference. A schema is a collection of database objects like a user. In the meantime, we call .DDL file as a Schema. Maybe one of them wrong or there're some relations between them. tks.