Start a new thread. Type whatever it is you have to say/ask in the top portion, just like starting a new thread regularly.
In the "Additional Options" section at the bottom of the page check "Yes, post a poll with this thread" and select the number of poll options.
Click "Submit" and it will take you to a second screen where you type in your question, and the choices for your poll. In the options section on that page you can set a time limit, allow multiple votes, and/or show who voted for what, as you see fit.