There are two important programs to control sound input and output:
Pavucontrol is a gui for Pulseaudio and stands for Pulseaudio volume control.
Alsamixer is a terminal based tui program to control audio in- an output. It works with ALSA (Advanced Linux Sound Architecture).
Both programs do more or less the same task. Pulseaudio sits on top of ALSA (Advanced Linux Sound Architecture). Changes in one program will be reflected in the other. Having both at our disposal is helpful for troubleshooting, as they work in slightly different ways.
To hear the input of a recording you make, you usually have to play it back in whatever program you're using.
But is there a way to hear the input directly, as if through a sound monitor?
Yes, there is, but not a very comfortable one. You have to enable a module of pulseaudio on the cli. Like so
> pactl load-module module-loopback
Beware that if you didn't set up you're stuff right, you might get a feedback loop that makes some weird noise. If, for example, you use your internal microphone and speakers on full whack on a laptop, for example, you will make your laptop screams like you just unleashed cyber hell or something.
To stop the sound monitoring, just type this on the cli:
> pactl unload-module module-loopback
Pierre-Louis Blanchard, 2021-08-12