In many (but not all) forums, registered users have permission to start polls. (if it were to get out of hand, permissions could be changed, though!)
To start a poll, before submitting a new thread, scroll down to the "Additional Options" panel. There, you'll see the 'Post a Poll' section. Click the check box, and enter the number of options the poll needs. Then, after you hit the 'Submit' button, you'll be given the opportunity to enter the poll info.