It's trying to find modules on server "someOldIP" using TCP/IP port number "portno" and logging into that server (CVS login, which may or may not be the same as OS login) as user "username".
Here's a typical connection
string:
:extssh:grodnik@cvs.mousetech.com:22/usr/local/cvsrepo
This would log user "grodnik" into the CVS repository /usr/local/cvsrepo on cvs.mousetech.com over port 22 using the ssh protocol. Actual CVS projects would then be subdirectories of /usr/local/cvsrepo.
I don't recognize the "sspi" protocol in your example. It's not one of the ones that shows up on my list when I create a new repository definition in Eclipse.
If your repository has been intialized by CVS (Eclipse expects to find an existing repository), an empty repo will contain a single module named CVSROOT, which keeps the parameters of the overall repository. Yes, CVS uses itself to keep archives of its own configuration!
To check a project into CVS, you'd select the Team/Share Project menu item and fill in the dialogs. The project would then get checked into CVS.
Checking a project out of CVS isn't much harder. The main thing is whether or not the CVS archive includes Eclipse project definitions (.project and .classpath) and whether you want to use them or use your own local definitions. Based on those criteria, you'd use either the basic "Check out" or "Check out as Project" options.
In CVS, tagging done by attaching a tag to project files. To do that, you'd right-click the file(s) in the CVS Repositories View and select the Tag As Version... or Tag Existing option. One allows the assignment of an initial tag, the other to move the tag to point at later versions of the files.