A subject can have an extra option: a poll.
If you want to create a poll, use:

You will find new fields:

You can allow one person to make multiple choices for your poll:

You can limit the number of choices for each participant (eg : 3 choices at the most).
To validate a choice the person has to check the box next to it:

To close a poll, click on the link « Close your poll » located under the poll box.
People will not be able to vote anymore and everyone will see the poll results.
You can re-open a poll only if you are the one who created it in the first place or if you hold the position of moderator or administrator.
You can proceed to a blank vote by clicking on "Display Results"

Once you have seen the poll results, you will not be able to change your vote.