Before you can start the visualizer you first need to select your audio input. You can select this on the first drop down menu. Your microphone and desktop audio should show up automatically here. For users on windows devices, any virtual audio cables will also show up in the input section. If you do not see your desired input, go to your input settings on windows (Settings, System, Sound) and make sure your input is shown there.
If you are looking to visualize your desktop audio you will need to install a 3rd party application that will be able to connect your software / desktop audio to SYQEL by creating a virtual audio input. The next step in this quick start guide will go over the process.