someone tell me how these new clan things work
You can join or make a clan. On the hiscores, it tells the amount of members in your clan, and how much total exp your clan has in all stats. At the clan camp, you can receive your clan vexilum (it's like a flag), and your clan cape. The cape can be customized only if you are the creator of the clan. Go south of Falador and you will find the clan camp.
Poll