Mix two inputs and send them to system output

[bratfizyk]

(Please forgive me if this is already answered somewhere. I bet it is, but can't find it, sorry)

I've started playing with sound on my machine recently and discovered Carla. In my setup I have a microphone built into a headset and another one that I can connect my guitar to:

Sometimes I want them both to be active at the same time so that I can speak and play at the same time. An example of a use case is a video call. Currently I have to swap between active inputs.

When I open Carla I can see this in Patchbay section:

I've played a bit with it and discovered that Audio Input represents the currently selected audio device.

Is it possible to see all my connected input devices and connected them to the Output?

Going forwards, I've spent some time in the Carla's website searching for documentation and I found this:

What's the best source of information when it comes to using Carla?