For Agile theme, the icons bundled with the theme are listed here -

Icons bundled with Agile/Austin/FitPro theme

To use the icons, you can use the WordPress shortcode 


[icon class="icon-heart"]


or you just insert a HTML markup like


<span class="icon-heart"></span>


or some prefer


<i class="icon-heart"></i>


to display the icon. The above link provides you with the class names to use to display the corresponding icon. 

These font icons can be styled in CSS for color and size. You can utilize the custom.css file or the Custom CSS tab in the options panel to insert styling information like this -


#my-section i { font-size: 32px; color: #333; }


Do look for some examples of the usage in the demo content provided with the theme.

Although I am not going to recommend it, theoretically you can use inline styling as well to scale the icon and color it like this -


<i class="icon-switch" style="color:blue; font-size:48px;"></i>