add custom Metabox in WordPress without any Plugin

// call the below all code into functions.php
// How to add custom Metabox in WordPress without any Plugin?

// Create the function to retrieve custom fields value
function fc_get_custom_field_jokes( $value ) {
	global $post;

    $custom_field = get_post_meta( $post->ID, $value, true );
    if ( !empty( $custom_field ) )
	    return is_array( $custom_field ) ? stripslashes_deep( $custom_field ) : stripslashes( wp_kses_decode_entities( $custom_field ) );

    return false;
}


// Register the Metabox for Post Type
function fc_add_meta_box_for_jokes() {

	add_meta_box( 'fc-meta-box-for-jokes', __( 'Custom meta box', 'textdomain' ), 'fc_meta_box_output_for_jokes', 'jokes', 'sides', 'high' ); //show in custom post
}
add_action( 'add_meta_boxes', 'fc_add_meta_box_for_jokes' );


// Metabox Output
function fc_meta_box_output_for_jokes( $post ) {
	// create a wp nonce field
	wp_nonce_field( 'fc_nonce_jokes', 'my_nonce_jokes' ); ?>

	<p>
		<label for="jokes_contributor_name"><?php _e( 'Contributor Name', 'textdomain' ); ?>:</label>
		<input type="text" name="jokes_contributor_name" id="jokes_contributor_name" value="<?php echo fc_get_custom_field_jokes( 'jokes_contributor_name' ); ?>" size="25" />
    </p>
	<p>
		<label for="jokes_contributor_state"><?php _e( 'Contributor State', 'textdomain' ); ?>:</label>
		<input type="text" name="jokes_contributor_state" id="jokes_contributor_state" value="<?php echo fc_get_custom_field_jokes( 'jokes_contributor_state' ); ?>" size="25" />
    </p>
	<p>
		<label for="jokes_contributor_city"><?php _e( 'Contributor City', 'textdomain' ); ?>:</label>
		<input type="text" name="jokes_contributor_city" id="jokes_contributor_city" value="<?php echo fc_get_custom_field_jokes( 'jokes_contributor_city' ); ?>" size="25" />
    </p>
	<p>
		<label for="jokes_contributor_des"><?php _e( 'Contributor Description', 'textdomain' ); ?>:</label>
		<textarea style="width:100%;height:100px" type="text" name="jokes_contributor_des" id="jokes_contributor_des" value="<?php echo fc_get_custom_field_jokes( 'jokes_contributor_des' ); ?>" size="25" ><?php echo fc_get_custom_field_jokes( 'jokes_contributor_des' ); ?></textarea>
    </p>

	<?php
}


// Save the Metabox values with Post ID
	function fc_save_metabox_jokes( $post_id ) {
// Stop the script when doing autosave
	if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;

// Verify the nonce. If is not there, stop the script
	if( !isset( $_POST['my_nonce_jokes'] ) || !wp_verify_nonce( $_POST['my_nonce_jokes'], 'fc_nonce_jokes' ) ) return;

// Stop the script if the user does not have edit permissions
	if( !current_user_can( 'edit_post' ) ) return;

// Save the Contributor Name Field
	if( isset( $_POST['jokes_contributor_name'] ) )
		update_post_meta( $post_id, 'jokes_contributor_name', esc_attr( $_POST['jokes_contributor_name'] ) );

// Save the Contributor State Field
	if( isset( $_POST['jokes_contributor_state'] ) )
		update_post_meta( $post_id, 'jokes_contributor_state', esc_attr( $_POST['jokes_contributor_state'] ) );

// Save the Contributor City Field
	if( isset( $_POST['jokes_contributor_city'] ) )
		update_post_meta( $post_id, 'jokes_contributor_city', esc_attr( $_POST['jokes_contributor_city'] ) );

// Save the Contributor Description Field
	if( isset( $_POST['jokes_contributor_des'] ) )
		update_post_meta( $post_id, 'jokes_contributor_des', esc_attr( $_POST['jokes_contributor_des'] ) );

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


// post type
add_action( 'init', 'create_post_type' );
function create_post_type() {
  register_post_type( 'jokes',
    array(
      'labels' => array(
        'name' => __( 'Metabox' ),
        'singular_name' => __( 'Product' )
      ),
      'public' => true,
      'has_archive' => true,
	   'supports'=> array(''),
    )
  );
}





// source link: http://tipstolearn.com/add-custom-metabox-wordpress-without-plugin.html