The Audio Player can be selected in the Main Panel selection, located in the left sidebar. It allows loading and playing audio and MIDI.
To load an audio or MIDI file, drag it onto the Audio Player, or click the browser icon to open the file browser and load from disk. Loading any of the files from the Demos folder will load both the audio and the respective MIDI. You can load .wav, .flac, .mp3, .aif, .aiff, .mid, and .midi files.
The player output is available as an input in the Audio Modulators and Layer Properties → Input. If you want to set up audio reactivity to a recorded song or an audio file, start by loading it into the player. Then handle it in the AMs and/or in the Layer Properties. See Loading your track and making visuals react to it and Using the Visualizers.