The title and sub-title fields can be anything you like with the sub-title being optional. They are what will show up as the Catalog name after you have finished adding it.
The catalog URL will be the network address of the machine running the calibre Content server and the port that calibre has been set to use for its content server. It should be very similar to the URL you have already been using from Safari to access the Content server. The only difference is that you want to add /opds to the end of the URL to get the OPDS style catalog. As an example on my machine I would use:
Code:
http://192.168.1.90:8787/opds/
as my machine's IP address is 192.168.1.90 and I have set up the Content server to use port 8787. Depending on how your network is set up you might be able to use the name of your machine in place of the IP address.
Once you have the entry set up correctly you should be able to use it to browse through your catalog and select books to be downloaded. You will have to decide if you prefer thus interface to your ebook library to the browser based one you can get from Safari.
As an aside it is also possible to use a calibre2opds generated OPDS catalog (see my sig) as an alternative to the Calibre Content Server. It all depends on whether you want to keep the Calibre Content server running ot not.