This is meant for anyone who wishes to use font awesome and is totally unaware of its working.
Font Awesome is a set of icon vector graphics which can be used with CSS of your choice.
First of all we need to know what all icons it contains. For this you can check the font awesome cheatsheet at fontawesome.io/cheatsheet/
Step 1: Include the font awesome in your web page of theme by adding
<link rel="stylesheet" href="path/to/font-awesome/css/font-awesome.min.css"/>
to the <head> section.
Step. 2: Call the font by its class from Cheatsheet.
<i class="fa fa-heart"></i>
will result in