When you are creating an agenda, simply add the Polling activity and select the poll you'd like to use from your existing library, or create a new poll. Once you save a poll, it gets added to your library of polls which you can use again and again in future events.
Upon creating a new poll, you can create a title and add your own custom questions and answers. To get different styles of answer choices, click on the dropdown menu and select the most appropriate option - it might be phrase, multiple choice, single choice, etc.
After you save the poll, you can visit the Polling tab to edit the poll again if needed.