Hi~.
to start with, literally i would say
a schema is equal to an user area ( where the user objects are stored).
So once you create a user, a schema is created (essentailly..a logical 
workarea is created). Then you grant the required priveleges or roles
to the user.
But on the contrary u can use 
CREATE SCHEMA to create multiple tables and views and perform multiple 
grants in a single transaction. CREATE SCHEMA is seldom used.

The following statement creates a schema named oe for the sample order-entry 
user oe, creates the table new_product, creates the view new_product_view, 
and grants SELECT privilege on new_product_view to the sample human resources 
user hr.

CREATE SCHEMA AUTHORIZATION oe
   CREATE TABLE new_product 
      (color VARCHAR2(10)  PRIMARY KEY, quantity NUMBER) 
   CREATE VIEW new_product_view 
      AS SELECT color, quantity FROM new_product WHERE color = 'RED' 
   GRANT select ON new_product_view TO hr; 

SQL> SHOW USER 
USER is "MAG"
SQL> CREATE SCHEMA AUTHORIZATION CRSCH
  2     CREATE TABLE new_product
  3        (color VARCHAR2(10)  PRIMARY KEY, quantity NUMBER)
  4     CREATE VIEW new_product_view
  5        AS SELECT color, quantity FROM new_product WHERE color = 'RED';
CREATE SCHEMA AUTHORIZATION CRSCH
*
ERROR at line 1:
ORA-02421: missing or invalid schema authorization identifier

SQL> CONNECT CRSCH/CRSCH
Connected.
SQL> SHOW USER
USER is "CRSCH"
SQL> CREATE SCHEMA AUTHORIZATION CRSCH
  2     CREATE TABLE new_product
  3        (color VARCHAR2(10)  PRIMARY KEY, quantity NUMBER)
  4     CREATE VIEW new_product_view
  5        AS SELECT color, quantity FROM new_product WHERE color = 'RED';

Schema created.
SQL> SELECT * FROM CAT;

TABLE_NAME                     TABLE_TYPE
------------------------------ -----------
NEW_PRODUCT                    TABLE
NEW_PRODUCT_VIEW               VIEW