Bootstrap includes 260 glyphs from the Glyphicon Halflings set. Glyphicons Halflings are normally not available for free, but their creator has made them available for Bootstrap free of cost.

w3schools.com has an article on Bootstrap Glyphicon Components.

At w3schools.com there is some example code.

<p>Envelope icon: <span class="glyphicon glyphicon-envelope"></span></p> 
<p>Search icon: <span class="glyphicon glyphicon-search"></span></p>
<p>Print icon: <span class="glyphicon glyphicon-print"></span></p>
glyphicon glyphicon-pencil
glyphicon glyphicon-user
glyphicon glyphicon-ok
glyphicon glyphicon-remove