Reference

Font Awesome Icon Insertion If you’d like to insert a Font Awesome icon somewhere it’s needed, the best option is via the fa() function. Should you need a PNG version of the icon, then fa_png() is best for that.
fa()	Generate Font Awesome icons as SVGs
fa_png()	Create a PNG version of a Font Awesome icon
fa_i()	Generate a Font Awesome <i> tag
Extras
fa_html_dependency()	Use a Font Awesome html_dependency
fa_metadata()	Get metadata on the included Font Awesome assets