Hello there!
When creating a new forum topic, there is an option underneath the text box that says 'Poll creation'. Click this tab and several blanks will appear.

Fill in 'Poll question' with the question you wish to ask and put your answer options in the 'poll options' text box. Separate each answer with a tap of the 'Enter' key. Continue to fix the options to your liking. At the submission of your post, your poll will also be posted. Be aware that you cannot post polls on oekaki drawings.
If you would like to create a poll on an already existing topic, simply edit the first post and follow the same instructions.
Hope this helps!