OAuth and servers

My understanding of OAuth is the following:

    - client sends request token during redirect to server
    - Server displays authorization screen to resource owner
    - Resource owner provides uid and pw (not passed to client)
    - Server sends access token back to client
    - clients then users the Access token to gain access to a 
      resource

Select allOpen in new window

So I want to learn how to write a web service using OAuth.

Is there a web site I can communicate with that uses OAuth for my web service.  Something like yahoo, google, etc.  But this woud probably require previous exchange of tokens.  

So do I actually have to write a server as well ?

I am writing a client, and need a server to communicate with, what is the easiest path from here ?

Thanks