Man this is a question that can not be answered simply, you should probably go read up on server and server tasks. A server can be used for a very broad array of functions, and it all depends on your needs for your network and your clients and of course your users.
What exactly do you want to know? What is it that you are looking to do? Like TLarkin said windows server is a very big topic of talk, its not the kind of thing you could just sum up in 2 sentences.
No, it would suck to use a server OS as a desktop OS. They are designed for multi tasking and distributing jobs and so forth, not for end users. Sure you could use it, but it would suck compared to a desktop OS.