When inside of a forum, clicking on "New Thread" or the image that represents that, will allow you to post. You need to fill in your information, a topic and a message, then click on the "Post New Thread" button to submit.
Yes, this is done the same as posting a new one, except that you must be in a thread, and you need to click "Post Reply" instead of "Post new Topic. Moderators may close a thread to disable members' replying it.
You can edit a post by clicking on the "Edit Post" button underneath your message. You can only edit your own posts and sometimes this feature is disabled.
Yes, click the "Edit" button on one of your own topics, and then select the "!Delete this post" check box, and click "Edit Post". You can not delete a post if it is the start of a new topic.
Yes you can insert an attachment with any of your posts. The file size of the attachment must be under PHP and your group's upperlimit. You can attach a file on the New Thread and Post Reply pages with the upload field.
You can create a poll by visiting the forum you want to post the poll in and click on New Poll. The screen following after you click the button is just like a normal new thread page but has an extra box for Poll Answers. You should enter one answer per line with a maximum of 10 answers all together and set whether this poll can be multiple choice.
You can vote on polls in threads by visiting the thread with the poll in it and selecting the option you want to vote for, then clicking the submit button. You can only vote on a poll once, so once you vote, you can not change your mind.
The Administrators or Moderators may edit or disable a poll.