Two approaches for adding dashicons in HTML, using WordPress native CSS.
<h2 class="dashicons-before dashicons-smiley">A Cheerful Headline</h2>
<h2><span class="dashicons dashicons-smiley"></span> A Cheerful Headline</h2>
Both would appear like this:
A Cheerful Headline
Obviously, further CSS would need to be added to make the icons appear the way you intended.
Reference Links
https://developer.wordpress.org/resource/dashicons/#arrow-left
