Adding postmetabox in custom post type

// Registers the new post type and taxonomy

function wpt_event_posttype() {
	register_post_type( 'events',
		array(
			'labels' => array(
				'name' => __( 'Events' ),
				'singular_name' => __( 'Event' ),
				'add_new' => __( 'Add New Event' ),
				'add_new_item' => __( 'Add New Event' ),
				'edit_item' => __( 'Edit Event' ),
				'new_item' => __( 'Add New Event' ),
				'view_item' => __( 'View Event' ),
				'search_items' => __( 'Search Event' ),
				'not_found' => __( 'No events found' ),
				'not_found_in_trash' => __( 'No events found in trash' )
			),
			'public' => true,
			'supports' => array( 'title', 'editor', 'thumbnail', 'comments' ),
			'capability_type' => 'post',
			'rewrite' => array("slug" => "events"), // Permalinks format
			'menu_position' => 5,
			'register_meta_box_cb' => 'add_events_metaboxes'
		)
	);
}

add_action( 'init', 'wpt_event_posttype' );

add_action( 'add_meta_boxes', 'add_events_metaboxes' );

// Add the Events Meta Boxes

function add_events_metaboxes() {
	add_meta_box('wpt_events_location', 'Event Location', 'wpt_events_location', 'events', 'side', 'default');
}

//How it Works
<?php add_meta_box( $id, $title, $callback, $page, $context, $priority, $callback_args ); ?> 

$id is “wpt_events_location”- or the html id that will be applied to this metabox.
$title is “Event Location”. This appears at the top of the new metabox when displayed.
$callback is the function “wpt_events_location” which will load the html into the metabox.
$page is “events”, the name of our custom post type.
$context is “side”. If you wanted it to load below the content area, you could put “normal”.
$priority controls where the metabox will display in relation to the other metaboxes. You can put “high”, “low” or “default”.

// Add the Events Meta Boxes

function add_events_metaboxes() {
	add_meta_box('wpt_events_date', 'Event Date', 'wpt_events_date', 'events', 'side', 'default');
	add_meta_box('wpt_events_location', 'Event Location', 'wpt_events_location', 'events', 'normal', 'high');
}

// The Event Location Metabox

function wpt_events_location() {
	global $post;
	
	// Noncename needed to verify where the data originated
	echo '<input type="hidden" name="eventmeta_noncename" id="eventmeta_noncename" value="' . 
	wp_create_nonce( plugin_basename(__FILE__) ) . '" />';
	
	// Get the location data if its already been entered
	$location = get_post_meta($post->ID, '_location', true);
	
	// Echo out the field
	echo '<input type="text" name="_location" value="' . $location  . '" class="widefat" />';

}

// Save the Metabox Data

function wpt_save_events_meta($post_id, $post) {
	
	// verify this came from the our screen and with proper authorization,
	// because save_post can be triggered at other times
	if ( !wp_verify_nonce( $_POST['eventmeta_noncename'], plugin_basename(__FILE__) )) {
	return $post->ID;
	}

	// Is the user allowed to edit the post or page?
	if ( !current_user_can( 'edit_post', $post->ID ))
		return $post->ID;

	// OK, we're authenticated: we need to find and save the data
	// We'll put it into an array to make it easier to loop though.
	
	$events_meta['_location'] = $_POST['_location'];
	
	// Add values of $events_meta as custom fields
	
	foreach ($events_meta as $key => $value) { // Cycle through the $events_meta array!
		if( $post->post_type == 'revision' ) return; // Don't store custom data twice
		$value = implode(',', (array)$value); // If $value is an array, make it a CSV (unlikely)
		if(get_post_meta($post->ID, $key, FALSE)) { // If the custom field already has a value
			update_post_meta($post->ID, $key, $value);
		} else { // If the custom field doesn't have a value
			add_post_meta($post->ID, $key, $value);
		}
		if(!$value) delete_post_meta($post->ID, $key); // Delete if blank
	}

}

add_action('save_post', 'wpt_save_events_meta', 1, 2); // save the custom fields



// Displaying the Metabox Information in a Template
<?php echo get_post_meta($post->ID, "_location", true); ?>

Ref: https://wptheming.com/2010/08/custom-metabox-for-post-type/