Creating a Service and Listener

I have recently installed Oracle Developer Suite 10g on my PC and am having difficulty accessing SQL Plus as I do not have a service set up. I have tried using the help but I am not familiar with networks and so cannot create a service or listener.

How do I find out what the default database is that is setup as you are expected to know the full path and the SID of the database.

Can anyone advise me how to setup my service and listener please as I find the help unhelpful as I have never been good with Networks!

Thanks