If you click on a section that doesn't have any topics or threads for what you want to say, just click 'start a new topic' in the top right of your screen and post your message.

Can I just add: PLEASE use the search function.
This applies mostly to general topics, not advice-seeking ones.

If there has already been a thread about your topic, people may be hesitant to reply or you may miss out on some valuable information, which can easily be accessed in one or two clicks.