It's in the "Welcome" email and PM that is sent to every new member.
Here's the bits that explain about access to the chat feature:
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As a new member to the forums you can access most things straight away, but to access these great additional site features you'll need to be a full member:
• Member Blogs - start and run your very own CC blog.
• Chat - easy to use real-time chat for instant communication with other CC'ers.
• Gallery - post your bike / event / ride pictures in the CC gallery and share them with the whole community.
• Downloads - share your data with the CC community and upload / download maps, GPS data, safety tips, and more.
• Members Map - add yourself to the ever growing worldwide CC member's map.
How do you become a full member?
It's easy - just get chatting on the forums. Once you've posted enough times into the forums (and it really doesn't take many posts at all) you'll be automatically upgraded to full membership with access to all the features of the site.
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Cheers,
Shaun