Install app to desktop pc, Fire-up browser that you like and go to that address on your desktop pc. If page doesn´t load then for some reason installer didn´t install it correctly or you might have Antivirus app or firewall app configured so that it blocks that partcular address on your local computer.

After you have managed to set up desktop pc (server here) then install app from maemo.org repositories to your n900 and launch it. It should detect your server automatically in your HOME network where computers can freely communicate with each other.