Place icons just about anywhere with the <i> tag.
To increase icon sizes relative to their container, use the fa-lg (33% increase), fa-2x, fa-3x, fa-4x, or fa-5x classes.
Use the fa-spin class to get any icon to rotate.
<i class="fa fa-spinner fa-spin"></i>
<i class= "fa fa-refresh fa-spin"></i>
<i class="fa fa-cog fa-spin" ></i>
<a class="btn btn-medium btn-success" href="#"> <i class="fa fa-refresh"></i> Refresh</a>
<a class="btn btn-medium btn-primary" href="#"> <i class="fa fa-shopping-cart icon-large"></i> Checkout</a>
<a class="btn btn-medium btn-warning" href="#"> <i class="fa fa-trash-o icon-medium"></i> Delete</a>
<a class="btn btn-medium btn-danger" href="#"> <i class="fa fa-cog"></i> Settings</a>
<a class="btn btn-medium btn-info" href="#"> <i class="fa fa-info"></i> More Info</a>
<ul class="fa-ul">
<li><i class="fa-li fa fa-check"></i> Lists</li>
<li><i class="fa-li fa fa-check"></i> Buttons</li>
<li><i class="fa-li fa fa-check"></i> Button groups</li>
</ul>