Unity Unet Online V.S. Local

I watched a few tutorials and read documentation. Can someone give me a link or description on how to make a online server game. I understand how the local works but I don't know how to implement a online version where people can find random people to play with. Without them having to know each other iP or port numbers etc.. Also how could I make a Online game where friends could host a match but not on local if that makes sense?