Once you're ready to join in, the best place to introduce yourself is probably in the event announcement topic for the first race you intend to compete in, both to say hello, and so that whoever imports the results after the event will recognise your forum name if it's different to your race name.
You can find a list of the events coming up at the top right of each page. Most things on the SimRacing.org.uk site are either clickable or have tool tips (small strips of information that come up when you hover you mouse cursor over the item), and many have both. If it looks interesting - point your mouse at it... and then click it.