A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.
Every ORACLE database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.
Each databases logically divided into one or more tablespaces One or more data files are explicitly created for each tablespace.
A schema is collection of database objects of a User.
Schema objects are the logical structures that directly refer to the database's data.
Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.