That's exactly what it means..Developing it means to put some content up there. Whether it be in the format of a Wordpress blog or some HTML pages or whatever. Obviously, you're going to want the website to reflect the domain name. If the domain has "forex" in it then it should probably be a website about forex - I mean it would only make sense, right?
If people tell you the domain would be worth something if it was developed then the quickest way to develop it would probably be to throw it on some hosting, put wordpress on it, and start designing it and writing content for it. Now you've got a "developed" site