Basic Icon Usage:

<i class="fas fa-star"></i> Normal
<i class="fas fa-star fa-2x"></i> 2x Size
<i class="fas fa-star text-warning"></i> With Color

Button with Icon:

<button class="btn btn-primary">
  <i class="fas fa-download"></i> Download
</button>

Animated Icon:

<i class="fas fa-spinner fa-spin"></i> Loading...
<i class="fas fa-heart fa-beat text-danger"></i> Beating

Brand Icons:

<i class="fab fa-facebook-f"></i> Facebook
<i class="fab fa-x-twitter"></i> X (formerly Twitter)
<i class="fab fa-instagram"></i> Instagram
<i class="fab fa-github"></i> GitHub