Polls are forms to put on the main page or on another page of your wiki. They are a way of gathering statistics about your users, or can be used for fun. For using polls an admin on your wiki has to enable it on the page "Special:WikiFeatures".
Here's an example of a poll and the code to create it:
<poll> Question Answer 1 Answer 2 Answer 3 </poll>
This code creates the following poll: