How do I create filters for custom post types?

This is how I did it. If you have your custom post type as “projects”, and your category as “airplane”.

If you’re not planning on using the pre-build loop you would make another one called loop-projects.php. However, it’s not necessary.

               <?php
                $args = array(
                    'numberposts'    => 5,
                    'post_type'      => 'projects',
                    'category_name'  => 'airplane');
                query_posts( $args );
                get_template_part( 'loop', 'projects' );
                wp_reset_query();
              ?>