How I can record voice here, I mean how I can use MacBook Air powered by Catalina as a dictophone?

You can record a voice the same way you'd record any audio track [like guitar] -- just create an Audio track and select a microphone as the input. You could use a regular mic attached to an interface, the computer's built-in mic, setting it in the Audio Preferences and Smart Controls panel [as shown below], or a USB mic -- I've attached a GarageBand course that covers recording with a USB mic [video #7].

But that's garageband. I asked how I can record my voice as a text file. Just like a dictophone on a mobile phone to save my thoughts. How I can save my thoughts to the Macbook memory? Recording words like recording videos to Mac here.

Thanks for the information, I save it for the use of gb. I found myself I can record voice by Quick Time Player, but I remember times ago I tried to listen to my voice from sd card and Mac opened to me Itunes. Can I save my thoughts by Itunes or in any other way? As on the QTP I can't use a pause, but I need to.

Any time you record your voice it's going to be an audio file, which would need to be played back in iTunes, QuickTime Player, or another DAW [like GB]. It sounds like what you're looking for is a Dictation feature, that would turn your speech into text -- see this: https://support.apple.com/guide/mac-help/use-dictation-mh40584/10.15/mac/10.15 I have no idea how well this works [or if it works at all], but I guess it's worth a try..

Thank you very much for the info about the Dictation feature! I didn't know I can get my speech as text, but definitely I will try it. Thanks again!!

Well, I tried it. It has not my language, so I can't use it. But thanks for anyway!

On the screenshot above, you are showing me devices output and input, but I have in both system setting, not as in yours. Are the system settings OK, too?

Yes, if you don't have an external interface then System Settings will use the built-in microphone and the computer's built-in speakers/headphone out and that's fine.