There are numerous built-in RSS feeds available through WordPress that can be added to your theme for visitors to subscribe to, all of which can be found here: https://codex.wordpress.org/WordPress_Feeds
To get your feed to display as a subscription option in modern browsers, one of the following lines of code can be added to the head of your current theme, or you can add all of the lines of code to provide multiple subscription options.
RSS 0.92 feed
<link rel="alternate" type="application/rss+xml" title="Subscribe to <?php bloginfo('name'); ?>" href="<?php bloginfo('rss_url'); ?>" />
RSS 2.0 feed
<link rel="alternate" type="application/rss+xml" title="Subscribe to <?php bloginfo('name'); ?>" href="<?php bloginfo('rss2_url'); ?>" />
Atom feed
<link rel="alternate" type="application/rss+xml" title="Subscribe to <?php bloginfo('name'); ?>" href="<?php bloginfo('atom_url'); ?>" />
