I chose enable flex on the already recorded audio (my vocal) and listened to the vocal but nothing happened. How that enable flex changes tempo of my audio track? And tempo also can be slower or quicker. How to choose certain tempo? Or doesn't enable flex work in vocals.. ?

Simply enabling Flex doesn't do anything, it just makes it possible for audio to follow changes you make to the Project Tempo (at the top), or for you to time-quantize audio (just like MIDI), or for you to manually make changes to the timing of individual notes in an audio recording, as you can with MIDI/Instrument recordings. In the attached GB course, video #25 talks about using Flex to quantize audio or manually edit the timing of notes in an audio recording. Keep in mind that if you don't need to do any of those things -- change global Tempo, quantize audio timing, or manually change audio timing -- then you don't need to use Flex. Here's a link to the Apple support page on using Flex in GB: https://support.apple.com/guide/garageband/edit-the-note-and-beat-timing-gbnd6cdb22be/mac As with many of the advanced features in GB, Flex doesn't work as reliably in GB as it does in Logic, but again, I guess that's the limitation of using a free entry-level DAW..

All my audio use will be a vocal. Is there a need to quantize vocal timing? Or time quantizing and manually change timing, are they only meant for audio instruments (as vocal is audio, too) ? I mean if my audio is a vocal, have I a need to use flex at all.. ? Or only with vocal I have nothing to do with flex.. ? Because on the video 25 is only seen audio instrument.

Flex can be used to time-shift any audio, instrument or vocal -- if there's a musical reason to change the timing of something then it can be done, but if there's no musical reason to mess with timing then there's no need to use Flex.

Which are musical reasons to change the timing with vocal? Please explain. I have no idea, and thus I don't know, will I use flex with my vocal, or not. If I know the reasons then I can decide, need I that flex, or not.

I mentioned the reasons to use Flex in a previous post: - If you're not happy with the timing of an audio track and you want the notes to sound at different times, then you could enable Flex and use the Time Quantize slider [as shown in the video] - If you're not happy with the timing of an audio track and you want some notes to sound at different times, then you could enable Flex and manually adjust the timing of sone notes [as shown in the video] - If you want to globally change the Tempo of the song, and have audio tracks automatically play at the new Tempo, that would be another reason to enable Flex I can't really be more specific than that, it depends on the particular musical parts you create and how you want them to sound. If you're satisfied with the timing of your audio recordings, then don't worry about Flex..

OK. Does timing mean adjustment of notes length and pitch and position? I mean, timing is just reorganizing the notes, right? And time quantizing means notes putting to the right gridlines, right? Do timing and time quantize are different things? You write enable flex helps manually adjust the timing of some notes. Is it different than pitch correction's manually changing pitch, which isn't available in garageband? You write if I want to sound the notes at different times. Does it mean changing the length and pitch and position of notes as then indeed notes are sounding differently?

Flex allows for changing the timing of notes, not the pitches. It lets you change the start points and lengths of individual notes; quantizing automatically moves notes to start on the nearest gridline, but you can also move notes by hand -- again, both techniques are shown in the video referenced in previous posts. Time quantizing does indeed mean moving notes to the nearest gridlines, though it will only work if the notes were played reasonably close to the correct gridlines in the first place. I don't know what you mean when you say "timing is just reorganizing the notes" -- timing is when the notes sound relative to the musical grid and to each other. It is of course different than pitch correction, since time and pitch are two different aspects of musical performance. If you need to learn more about musical rhythm, you can check out this course: https://www.macprovideo.com/course/musictheory103-rhythm?afid=E470KLQ7r9 Beyond that you just have to listen to a lot of music and pay attention to the timing and rhythm of the musical parts, and then relate that to the musical parts you create..