I have notes synced via Tomboy Web.
Now I reinstalled my system and I am trying to setup but it requires me to connect to a Server.
What is the server's name?
I'm fairly sure the server used to be Ubuntu One, but that feature has been removed. You can use your own server if you have access to one. Another option is to sync Tomboy with a local folder which in turn syncs with Ubuntu One (or Dropbox, or any other cloud service).