Let's take our standard image here (fa-bomb):
Code:
<i class="fa fa-bomb"></i>
Now to make it start rotating you would simply add this
Code:
<i class="fa fa-spin fa-bomb"></i>
See how I added fa-spinner. That makes it spin!
Here you can see how this looks: http://jsfiddle.net/NBB_NSA/cqzjsLze/3/