Find one and try it out, it really is easy to get started.
One way to start is with a local evening 10, many clubs run these from about mid-April through to mid August. Usually a couple of pounds to enter and you don't normally need to join the club to do your first one (if you are already a member of a CTT-affiliated club then you won't need to join the hosting club).
Or you can try an open event, it'll be a few pounds more and will probably take place on a Saturday afternoon (nice) or really early on a Sunday morning (at least you get the rest of the day free).
I didn't do any training before my first one- this has the advantage that when you do start training you make rapid progress. If you have an event targetted in, say, May you may want to start doing some harder efforts once or twice a week a few weeks before the event. You can be as low-tech or scientific with your training as you want, there's plenty of advice on the web.
Bet you won't be dead last.
Also look here:
CTT