Simply launch the app and run through the audio setup wizard. If your OS supports it, you can simply click [here](mumble://nixnet.xyz:64738) and it will open automatically and connect to the server. Alternatively, launch Mumble, go to `Server -> Connect -> Add new`. Enter whatever username you want, use `nixnet.xyz` as the address, `64738` for the port, and label the server however you'd like.