As audio clips contain the sound (and MIDI) files you are using in your Qtractor project, so do Tracks contain the clips themselves. Tracks allow you to mix the audio clips in relation to one another, apply effects to whole groups of clips without ever affecting the waveform files themselves (ie, non-destructively), and even automate everything from volume to panning to the functions of effect units and synths.

A special window is dedicated to managing tracks: the Mixer window; set up like a traditional mixing desk with a user-friendly interface to allow for Aux Sends, Returns, Sub-mixing, and more. You can also manage many aspects of your tracks through the track list on the left of the Qtractor interface, but since the Mixing desk interface is so ubiquitous and useful, it's common to have it open on a separate monitor or virtual desktop for quick reference.

To open the Mixer window, click on the View menu, select Windows, and choose Mixer.