How do I create a table when a module is installed?

I want to add a custom table when a module I develop is installed. The code I am using doesn’t seem to work, as the post table isn’t created.

What is wrong with the code I am using?

/**
 * Installs the database schema.
 */
function mymodule_install() {
  drupal_install_schema('post');
}

/**
 * Uninstalls the database schema.
 */
function mymodule_uninstall() {
  drupal_uninstall_schema('post');
}

/**
* Creates the tables using the schema API.
*/
function mymodule_schema() {
  $schema['post'] = array(
    'description' => 'description pour la table post',
    'fields' => array(
      'pid' => array(
        'description' => 'post id',
        'type' => 'int',
        'not null' => TRUE,
      ),
      'title' => array(
        'description' => 'title',
        'type' => 'varchar',
        'not null' => TRUE,
      ),
      'body' => array(
        'description' => 'body',
        'type' => 'varchar',
        'not null' => TRUE,
      ),
      'created' => array(
              'description' => 'created',
              'not null' => TRUE,
              'mysql_type' => 'timestamp',
            ),
      'primary key' => array('pid'),
    ),
  );
}