Airport Time Capsule Server?

I just recently bought a 3tb airport time capsule from apple. I came across the subject with someone there... not employee, another shopper that you could use it as a media server. Whereas I could access it from anywhere outside of home to connect to and get my media. Most importantly is my iTunes library. I have a 15'' RMBP with only 256gb of ssd. Found videos on the Youtube and i see its possible and but I'm having no luck. can someone shed some light here? One more thing, how do i backup only what i want to the tc?