Function Reference/ add theme support

/*Description
===============*/

Allows a theme or plugin to register support of a certain theme feature. If called from a theme, it should be done in the theme's functions.php file to work.

/*Usage
===============*/

<?php add_theme_support( $feature ); ?>

/*Parameters
=============*/

$feature
(string) (required) Name for the feature being added.

        Features list:

         *^*   'post-formats'
         *^*   'post-thumbnails'
         *^*   'custom-background'
         *^*   'custom-header'
         *^*   'automatic-feed-links'
         *^*   'menus'

        ***Default: None

/*Examples
=============*/

 ^*^ Post Thumbnails

This feature enables Post Thumbnails support for a Theme.

add_theme_support( 'post-thumbnails' );
add_theme_support( 'post-thumbnails', array( 'post' ) );          // Posts only
add_theme_support( 'post-thumbnails', array( 'page' ) );          // Pages only
add_theme_support( 'post-thumbnails', array( 'post', 'movie' ) ); // Posts and Movies

set_post_thumbnail_size( 200, 200, true );             // Sets the size of thubnails
add_image_size( 'post-image', 150, 150, true );       // Sets the size of Post-Images


Codes must be inside <?php?> Tag.This feature must be called before the init hook is fired. That means it needs to be placed directly into functions.php.