WordPress makes it so easy to display external RSS feeds anywhere in your theme.
To display, say, the RSS feed for WP-mix in your sidebar, open your theme’s
sidebar.php file and add the following code:
<?php include_once(ABSPATH.WPINC.'/rss.php'); wp_rss('https://wp-mix.com/feed/', 5); ?>
This will display the latest 5 posts from the specified feed. Customize to suit your needs.