Could you please explain me how it works with Ripple, XRP and when XRPis used. So far I understand that banks can use the software of Ripple, so far so good, but when do they need to use XRP and why is there such a high volume in XRP trading?

I mean how can you fake a marketcap of 8 billion dollar in XRP, there mus be something wich is working out for XRP. Thanks