What are the difference between DDL, DML and DCL commands?

DML
Data Manipulation Language (DML) statements are used for managing data within schema objects. Some examples:
SELECT - retrieve data from the a database
INSERT - insert data into a table
UPDATE - updates existing data within a table
DELETE - deletes all records from a table, the space for the records remain.
DDL
Data Definition Language (DDL) statements are used to define the database structure or schema. Some examples:
CREATE - to create objects in the database
ALTER - alters the structure of the database
DROP - delete objects from the database
TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed
COMMENT - add comments to the data dictionary
RENAME - rename an object
CREATE,ALTER,DROP AND TRUNCATE ARE CALLED DDL COMMANDS. They are called Data Definition since they are used for defining the data. That is the structure of the data is known through these DDL commands.
DCL
Data Control Language (DCL) statements. Some examples: GRANT - gives user's access privileges to database.
REVOKE - withdraw access privileges given with the GRANT command.