Adding Post Thumbnails

I’m using a magazine style theme, the landing page is using ‘excerpts’ and showing the top 6 posts. I’m trying to add the thumbnail so show with the excerpt on the landing page. I’ve add the theme support string, but not seeing the thumbs or the feature image box in my edit posts page. Below is how I currently have it written: Do I need to additionally write from another script, or add something to this function.php page?

/** Add theme support for Feed Links. */
	add_theme_support( 'automatic-feed-links' );

	/** Add theme support for Custom Background. */
	add_theme_support( 'custom-background', array( 'default-color' => 'fff' ) );

	/** Set content width. */
	chiron_set_content_width( 640 );

        <strong>/** Add theme support for Post Thumbnail. */
        add_theme_support( 'post-thumbnails' );</strong>

	/** Add custom image sizes. */
	add_action( 'init', 'chiron_add_image_sizes' );

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