How do I post a new topic?

So you want to open a new topic, cool!
Here's how to do it:

Browse to the board where you wish to post and click the New Topic button (positioned by default at both the top and the bottom of the board, as shown in the User Help Introduction), which should take you to the Start new topic screen.
While this presents a number of options, the two most important are the Subject field and main Message field (not labeled as such, but obvious by its size). So enter your subject and start to type (or paste) your message into the main text area, noting that a message missing either a subject or a body will not be accepted for posting until it has both. If you're happy with your plain text message, you can then post it by clicking the Post button and/or preview it first by clicking the Preview button, but there are many further options available to make things that little bit more interesting.

The additional options can be reached by clicking Additional Options... directly under your post.
The options you'll be presented with:

Notify me of replies
Check this to subscribe to email notification for the topic.

Return to this topic
Check this to return to the topic (instead of the message index) after posting (NB you can also set this behavior as a preference in your profile).

Don't use smileys
Check this to prevent certain character combinations in your post from being parsed and rendered as smileys.

Attachments
Allows you to attach files to your posts in much the same way as most email clients, so you simply have to browse to the relevant file(s) on your computer before clicking Post. You can delete your attachment(s) or add more by modifying your post, but please note that it's not possible to preview attachments so you should always browse to and attach your files just before you finally post your message.