The tribe is called creativecoin, you can use its own front end which will add the tag automatically, or you can just use it literally as a tag like how you normally add tags to a post (easiest way if you're particularly attached to whatever front end you're using).

ccc is a steem engine token and you can buy or sell it on there for steemp (steem peg which can be traded for steem or a whole pile of other tokens that have cropped up with the tribes). I'm pretty sure they're only tradable on steem engine at this point and have no idea if there's any plans to put them on anything else, but they can be traded for steem so I guess you can indirectly? You should just be able to log in to steem engine with your posting key so maybe poke in and have a look around.

Tribes and the steem engine tokens seem to have been what happened when some people got too impatient waiting around for communities and SMTs to happen if that helps :)