Tooltips comprise of several attributes that can be added to most elements, a class of "has-tooltip", the "data-toggle" attribute which must contain "tooltip" and the "data-title" attribute that contains the text that should be visible in the tooltip.
<a href="#" class="has-tooltip" data-toggle="tooltip" data-title="This is a tooltip">
This has a tooltip
</a>
So does this
<span class="has-tooltip" data-toggle="tooltip" data-title="Another tooltip">
So does this
</span>