Participating in a running event is like an inevitable process for any runners, be it a 5k fun run, or a 10k slow jog, just being part of it is a good experience for any beginners. There is no sport that can allow you to compete if you cannot prove a good record, but not for running, there are alot of organisations who are more than willing to organise such events, even it's just a marketing gimmick, it is also an opportunity to see the results of your training.

A route is usually pre-planned for the running event, and depends on the theme, you may encounter different terrain or some unusual evironment, you may even get to run in places normally closed for runners, like on an expressway, runways or tunnels. So far my best experience is in Sedona, when they were having their 2nd annual Marathon Event.

If you just started running and thinking when is the best time to join a running event, you might want to choose a major running event with a longer distance as target. First time runners usually achieve better results than they expected, so don't waste your virgin run. First timer will usually be motivated to do well, in terms of endurance, stamina, pace and timing, even diet and knowledge of the sport suddenly seems to strike an interest in your daily life. You will also start to observe certain parts of your body is stronger or weaker, and cross trained that weak link to achieve longer distance and better timing.

My recommendation for starters is to join a 10K run, and the training routine should include 5K long distance runs, without feeling much stress on your body.