custom post type index page

If you have:


register_post_type( 'my_custom_post_type', $args );


And you need a custom page to displays all entries from this custom post type, you have to create: archive-my_custom_post_type.php.
But if you don’t need a custom page, wordpress will use archive.php to display you custom post type archive.

If you only need to customize the entry page, you have to create: single-my_custom_post_type.php

Where are you creating the custom post type, in theme functions.php or using a plugin?

If using functions.php, you need to create archive-my_custom_post_type.php or single-my_custom_post_type.php in theme’s folder.

If using a plugin, you need to create archive-my_custom_post_type.php or single-my_custom_post_type.php in plugins’s folder and point wordpress to read it, so include this function in your plugin:

function get_custom_post_type_template($template) {
    global $post;

    if ($post->post_type == 'my_custom_post_type') {
        $template = dirname( __FILE__ ) . '/archive-my_custom_post_type.php';
    }
    return $template;
}

//add_filter( "single_template", "get_custom_post_type_template" ); //for single page
add_filter( "archive_template", "get_custom_post_type_template" ); //for archive