this snippet code is about adding custom post-type and custom taxonomy in WordPress theme and use in function.php

function.php

<?php
//Creat a new taxonomy Booking Categories
function sin_taxo(){
	register_taxonomy( 'booking_category', 'booking', 
		array(
			'labels' => array(
				'name' => __('Booking Categories'),
				'singular_name' => __('Booking Category'),
				'add_new' => _x('Add New Category' , 'booking-category'),
				'add_new_item' => __('Add New Category'),
				'search_item' => __('Search Booking Category'),
				'all_items' => __('All Booking Categories'),
				'parent_item' => __('Parent Booking Category'),
				'parent_item_colon' => __('Parent Booking Category')
			),
			'hierarchical' => true,
			'public' => true,
			'show_ui' => true,
			'show_admin_column' => true,
			'rewrite' => array('slug' => 'booking-category'),
			'capabilities' => array(
				'manage_terms' => 'manage_categories',
				'edit_terms'   => 'edit_categories',
				'delete_terms' => 'delete_categories',
				'assign_terms' => 'assign_categories',
			),
			'show_in_rest' => true,
			'rest_base' => 'categories',
			'rest_controller_class' => 'WP_REST_Terms_Controller',
		));
}

add_action('init', 'sin_taxo');

//Add Booking post_type

function booking_post_type() {
	register_post_type('booking' ,
		array(
			'labels' => array(
				'name' => __('Bookings'),
				'add_new' =>  _x('Add New' , 'booking'),
				'add_new_item' => __('Add New Booking'),
				'all_items' => __('All Bookings')
			),
			'public' => true,
			'has_archive' => true,
			'menu_position' => 5,
			'menu_icon' => 'dashicons-calendar-alt',
			'capabilities' => array(
				'edit_post'          => 'edit_booking', 
				'read_post'          => 'read_booking', 
				'delete_post'        => 'delete_booking',  	
			),
			add_post_type_support('booking' ,
				array(
					'title','editor','author','excerpt','trackbacks','custom-fields','comments','revisions', 'thumbnail')
			),
			'taxonomies' => array(booking_category , post_tag),
			'has_archive' => true,
			'rewrite' => array(
				'slug' => 'bookings',
				'with_front' => true,
				'feeds' => true,
				'pages' => true,
			),
		)
	);
}
add_action('init', 'booking_post_type');
?>