To connect to WebTV using the WebTV for Dreamcast disc, you must first set up your Dreamcast to connect to the Internet. Using landline is the easiest right out of the box, as every model of the Dreamcast comes with a 56K dial-up modem card attached to the console. This guide applies to all set-ups, but assumes that you have set up your preferred connection using the guides above, excluding landline of course. First things first, you need a way to actually run the WebTV for Dreamcast disc on the console, which can be achieved in two ways, for Anglophones: Burn this Dreamcast disc image to a rewritable CD, or copy it to the SD-card you use for your GDEmu, assuming you have one. Once you have set-up your preferred way of connecting, and burned/copied the disc image to whatever it is you're using, put the disc or SD-card into your Dreamcast, and turn it on. You should see a Microsoft WebTV splash screen. Now, this part is important.
Unplug the phone line from the back end of the Dreamcast, if it was plugged in, and select "Connect to WebTV" at the bottom. Allow it to "dial", and error out. Now, when it errors, go to dialing options, go into Basic, and disable pulse dialing. Plug the phone line into the back end of the Dreamcast, and try dialing again.
With any luck, your console should dial into the Redialed access number, and connect. You should be taken to a registration screen after connecting. From here, follow the instructions. Upon finishing registration... That's it! You have successfully connected to WebTV Redialed!