Are you using some kind of hosting company's graphical configuration ? It sounds like you should not have made www.abc.com forward to itself, and that you are probably ok now, but it's hard to tell.
To really know what is going on here, we would need to know more details -- for instance, by "domain forwarding" do you mean a CNAME record, or a rewrite rule on an apache web server ?
Also, can any cgi code running on abc.example.com tell what name the browser is being used to reach it ? This might matter for the code you use to run the site.
You can educate yourself about these issues without learning everything in the world about the internet, and if you are going to be making money from web sites that would probably be a good idea.
To really know what is going on here, we would need to know more details -- for instance, by "domain forwarding" do you mean a CNAME record, or a rewrite rule on an apache web server ?
Also, can any cgi code running on abc.example.com tell what name the browser is being used to reach it ? This might matter for the code you use to run the site.
You can educate yourself about these issues without learning everything in the world about the internet, and if you are going to be making money from web sites that would probably be a good idea.