This plugins adds a shortcode for embedding polls from Twtpoll really easy.
You have to specify the ID of your poll to display it. You can do this with the attribute "id", eg. [twtpoll id="d6iby3"]
Go to your poll in Twtpoll and look at the URL in the address bar of your browser. The last part is the ID you need for embedding it. Just copy and use it.