CREATE TABLE

CREATE TABLE [schema.]table
                  (column datatype [DEFAULT expr][, ...]);

-  Immediate effect on the database.
-  record record information in the data dictionary.

schema              is the same as the owner's name
table                   is the same name of the table
DEFAULT expr     specifies a default value if a value is omitted in the INSERT statement.
column               is the name of the column
datatype             is the column's data type and length

** schema **
A schema is a collection of objects. Schema objects are the logical structures that directly refer to the data in a database. Schema objects include tables, views, synonyms, sequences, stored procedures, indexes, clusters, and database link.

ex) SELECT * FROM user_B.employees;
    SELECT * FROM user_A.employees;