Add Custom Post on WordPress with function.php

You can add custom post with category/taxonomy option on WordPress

add_action( 'init', 'design_taxonomy');


# Registering Custom Market Type Post
add_action( 'init', 'register_design_post', 20 );
function register_design_post() {
	$labels = array(
		'name' => _x( 'Design Post', 'design_post','custom' ),
		'singular_name' => _x( 'Design Post', 'design_post', 'custom' ),
		'add_new' => _x( 'Add New', 'design_post', 'custom' ),
		'add_new_item' => _x( 'Add New Design Post', 'design_post', 'custom' ),
		'edit_item' => _x( 'Edit Design Post', 'design_post', 'custom' ),
		'new_item' => _x( 'New Design Post', 'design_post', 'custom' ),
		'view_item' => _x( 'View Design Post', 'design_post', 'custom' ),
		'search_items' => _x( 'Search Design Post', 'design_post', 'custom' ),
		'not_found' => _x( 'No Design Post found', 'design_post', 'custom' ),
		'not_found_in_trash' => _x( 'No Design Post found in Trash', 'design_post', 'custom' ),
		'parent_item_colon' => _x( 'Parent Design Post:', 'design_post', 'custom' ),
		'menu_name' => _x( 'Design Post', 'design_post', 'custom' ),
	);

	$args = array(
		'labels' => $labels,
		'hierarchical' => false,
		'description' => 'Design Posts',
		'supports' => array( 'title', 'editor', 'excerpt', 'author', 'thumbnail', 'comments', 'revisions', 'post-formats', 'custom-fields' ),
		'taxonomies' => array( 'design_tag','design_categories'),
		'show_ui' => true,
		'show_in_menu' => true,
		'menu_position' => 5,
		'menu_icon' => "dashicons-buddicons-replies",
		'show_in_nav_menus' => true,
		'publicly_queryable' => true,
		'exclude_from_search' => false,
		'query_var' => true,
		'can_export' => true,
		'public' => true,
		'has_archive' => 'design',
		'capability_type' => 'post'
	);  
register_post_type( 'design_post', $args );//max 20 charachter cannot contain capital letters and spaces
}

add_action( 'init', 'flush_on_init' );
function flush_on_init(){
	flush_rewrite_rules();
}

How to show the post

  <div class="container clearfix">

    <div class="row">

      <?php

      $args = array(
        'posts_per_page'   => 12,
        'orderby'          => 'date',
        'order'            => 'DESC',
        'post_type'        => 'post', 
        'post_status'      => 'publish',
        'paged' => get_query_var('paged') ? get_query_var('paged') : 1
      );

      $the_query = new WP_Query( $args );

      query_posts($args);

      if ( $the_query->have_posts() ) :
        while( $the_query->have_posts()):$the_query->the_post(); ?> 


          <div class="col-sm-6 col-md-4 col-lg-4">
            <div class="news-back">
              <div class="row up">
                <div class="col-sm-12 ">
                  <div class="news-bg-wrap">
                    <?php the_post_thumbnail(); ?>
                  </div>
                </div>
              </div>
              <div class="row down">
                <div class="col-sm-12 text">
                  <p class="title"><a href="<?php the_permalink(); ?>"> <?php the_title(); ?></a></p>
                  <div class="post_excerpt"><?php echo strip_tags(post_excerpt(10)); ?>.....</div>
                  <div class="readmores"><a href="<?php the_permalink(); ?>">Read More</a></div>
                </div>
              </div>     
            </div>
          </div>

          <?php       
        endwhile; ?>

      </div>

      <div class="row">
        <div class="col-lg-12">
          <?php the_posts_pagination(
            array(
              'prev_text' => '<',
              'next_text' => '>',
              'screen_reader_text' => ' '
            )
          ); ?>
        </div>
      </div>
      
    <?php endif;  
    wp_reset_query();
    wp_reset_postdata();?>


  </div>