geoff, to explain a little further, it is the domain name, e.g. paypal.com, mudcat.org that points you to where a site is. The bit to the left of :// just gives the protocol. http (hypertext transfer protocol) is the usual one for web pages. https is using SSL (secure socket layer).

It's quite possible to have different servers/ phyisical machines on a domain, e.g. www.folkinfo.org, mail.folkinfo.org and ftp.folkinfo.org are all on different machines but they all come under the general setup of folkinfo.org.