Working with Audio in 5 steps
Step 1
Add some tracks with Ctrl+T.
Tracks are polymorphic and can contain any sort of data (audio, video, midi etc). You do not need to add an "audio track" or a "midi track". In addition, there are no "mono" or "stereo" tracks. If a part contains more than one audio channel, then this track is converted to a "stereo" track. A track can have any number of channels, not restricted to 1 or 2.

Step 2
Press F9 to review the track routing.
Turbo Play configures this for you automatically. This is to specify which track goes to which output and from which input the track receives audio data. A track can receive input from more than one inputs and can output to more than one outputs. If a track has multiple channels, you can configure i/o per channel.

Step 3
Add some parts to each track by double clicking at the track space, then double click the part to edit it.
Parts which contain audio can contain MIDI (pianoroll, score, byzantine, drum loop) or audio data. You can edit audio parts by double clicking on them with the audio editors: AudioPiano RollScoreByzantineLoopStyle PlayerFlow

Step 4
Press F3 to use the mixer.
The Mixer configures the tracks, volume, gain, effects and more.

Step 5
Use the Import button to import stuff, use the Export button to export stuff.
This includes audio, midi etc. Check importing and exporting data, and the supported media files.