A poll represents the Zigpoll you will see on the page. You can have as many polls as you like within your account. Each poll contains a collection of Slides in some order. A slide can be variety of things like a question, a statement, or an email capture form. You can learn more about Slides here:
By default all polls are hidden. This is done intentionally so that you can make the poll exactly how you want it before showing it to your customers. When you switch a poll to be visible it will be come public for all to see. You can preview your poll while it is invisible to make sure it works the way you want before going live.