Visitor log-ins and new topics

Hi, I am sure this is going to seem like a rather stupid question, but nevertheless, I can’t work it out!!!! I can’t work out how to add the fields into the blog that allow visitors to add new topics..and there is also that bit about “you must be registered/logged-in to comment” or words to that effect!!! That’s not appearing anywhere either! At the moment, visitors can only leave comments on existing posts (that I have done). Can someone indulge me please!!!