Clearly, you can make a post in this thread, so you can do replies?
To start a new thread (or topic), go to the forum that you want to make it in, and on the left just below a list of forums is a button saying "+ Post New Thread". Click this and it will let you create a post with a title and polls, etc.
You cannot edit, due to a severe glitch in forum signups.
If you can't see the button to post a new thread (it looks like the "+ Add New Reply" at the top of this thread), then it's quite possible that it's in a forum where only Admins can post. In that case, try it in a different forum.
Hope this helped!