As we saw Usine has unique routing capabilities. If you feel lost with a routing open the Synthetic view to display an overview of all audio and MIDI flows.
With a simple click on each item you have an access to all levels that you can set very quickly. For example a click on the Monitor 1 output audio device, let you you adjust all sources levels redirected to it.
Here, an example of rack (which contains a sample player) connected to a simple audio output device.
Here, a delay rack receives the previous rack (with the sampler) and outgoing in an audio output.