How do I post a topic in a forum?
Easy -- click the relevant button on either the forum or topic screens. You need to register before you can post a message. The facilities available to you are listed at the bottom of the forum and topic screens (the "You can post new topics", "You can vote in polls", etc. list)
How do I edit or delete a post?
Unless you are the board admin or forum moderator you can only edit or delete your own posts. You can edit a post (sometimes for only a limited time after it was made) by clicking the edit button for the relevant post. If someone has already replied to the post, you will find a small piece of text output below the post when you return to the topic that lists the number of times you edited it. This will only appear if no one has replied; it also will not appear if moderators or administrators edit the post (they should leave a message saying what they altered and why). Please note that normal users cannot delete a post once someone has replied.
How do I add a signature to my post?
To add a signature to a post you must first create one; this is done via your profile. Once created you can check the Add Signature box on the posting form to add your signature. You can also add a signature by default to all your posts by checking the appropriate radio box in your profile. You can still prevent a signature being added to individual posts by un-checking the add signature box on the posting form.