Add Featured Posts and display front-end

//ADD ALL FUNCTIONS IN functions.php FILE
function sm_custom_meta() {
    add_meta_box( 'sm_meta', __( 'Featured Posts', 'sm-textdomain' ), 'sm_meta_callback', 'post' );
}

function sm_meta_callback( $post ) {
    $featured = get_post_meta( $post->ID );
    ?>

	<p>
    <div class="sm-row-content">
        <label for="meta-checkbox">
            <input type="checkbox" name="meta-checkbox" id="meta-checkbox" value="yes" <?php if ( isset ( $featured['meta-checkbox'] ) ) checked( $featured['meta-checkbox'][0], 'yes' ); ?> />
            <?php _e( 'Featured this post', 'sm-textdomain' )?>
        </label>

    </div>
</p>

    <?php
}
add_action( 'add_meta_boxes', 'sm_custom_meta' );

//IT WILL SAVE META

function sm_meta_save( $post_id ) {

    // Checks save status
    $is_autosave = wp_is_post_autosave( $post_id );
    $is_revision = wp_is_post_revision( $post_id );
    $is_valid_nonce = ( isset( $_POST[ 'sm_nonce' ] ) && wp_verify_nonce( $_POST[ 'sm_nonce' ], basename( __FILE__ ) ) ) ? 'true' : 'false';

    // Exits script depending on save status
    if ( $is_autosave || $is_revision || !$is_valid_nonce ) {
        return;
    }

 // Checks for input and saves
if( isset( $_POST[ 'meta-checkbox' ] ) ) {
    update_post_meta( $post_id, 'meta-checkbox', 'yes' );
} else {
    update_post_meta( $post_id, 'meta-checkbox', '' );
}

}
add_action( 'save_post', 'sm_meta_save' );

//DISPLAYING IT IN FRONT-END
$args = array(
        'posts_per_page' => 5,
        'meta_key' => 'meta-checkbox',
        'meta_value' => 'yes'
    );
    $featured = new WP_Query($args);

if ($featured->have_posts()): while($featured->have_posts()): $featured->the_post(); ?>
<h3><a href="<?php the_permalink(); ?>"> <?php the_title(); ?></a></h3>
<p class="details">By <a href="<?php the_author_posts() ?>"><?php the_author(); ?> </a> / On <?php echo get_the_date('F j, Y'); ?> / In <?php the_category(', '); ?></p>
<?php if (has_post_thumbnail()) : ?>

<figure> <a href="<?php the_permalink(); ?>"><?php the_post_thumbnail(); ?></a> </figure>
<p ><?php the_excerpt();?></p>
<?php
endif;
endwhile; else:
endif;