If I have put to comparing the multiple take, how can I remove the comparing?

I'm not entirely sure what you're asking there, but if you mean how do you get rid of the multiple Take tracks in GarageBand after you've finished the Comp, then you could just mute or delete those extra tracks -- I wouldn't delete them, I'd just mute them, in case you change your mind and want to go back and re-do the comp at a later date..

No, not about a comp. I mean, if i have splitted the region for comparing and want to get back the whole region (not comparing or with other words, not splitted one) how to I get back the original unsplitted one? Cmd j? But if I did so, the notes disappeared at all, although they were there before. What is that, why they are disappearing and how to get back original long (normal) region with its notes, as it originally was? The video is included. https://youtu.be/o-PThl-V4W0 And firstly on the first part of splitted region the notes disappeared, too. If I remember rightly.

For what you tried to do, that result is normal -- after you've cut a Region and moved it to the Comp track, dragging an end back out won't restore the notes that were there in the original Region. That's why I recommended that you NOT delete the extra Take tracks, only Mute them, in case you want to go back to those original notes/parts. On an unrelated matter, you should not be getting a "Circular Structure" message frequently. It may indicate corruption in a particular Project, which could potentially cause unexpected behavior/problems. If you get that message in more than one Project, you should contact Apple/GarageBand Tech Support..

I don't delete extra tracks. I don't know, how to do it. If I already have the comp, all I am doing and thus my notes disappearing, I choose command j. I choose it as I think that command j unites the splitted region to the original region (an one piece region I mean only take 3 was seen in the video). He shows on the video how to split the region and make from that a comp track, but he doesn't show how to get rid of that splitted (comp) one back to the original region. That circular structure appears when I hit command j. I now understand, I can't make original region from comp, as originally there was only 1 and same take is seen, but now 2 different takes are seen. And he also didn't tell anything about cmd j. It is my mind figured it out. The video ends with comp track. How can I get rid of that comp one to get back to the original region (original region - on his video only take 3 was on the region). Does the command j is an option, or not? Or what to do ? Does command j is a deleting option ( you say I delete the extra take tracks)?

If you use the method shown in the video, you CAN'T get back to the original multi-take Region after comping -- you would have to use the method I described [keeping/muting the extra Take tracks], NOT the method shown in the video, if you want to be able to go back after the fact and change the Comp. And even with my suggested method, apparently you still can't make a cut-up Take into one long Region again after you've cut it up, though you can retain & reuse all the pieces of each individual Take if you've *Copied* the desired sections to the Comp track and kept all the individual pieces of all the Take tracks. As I said, Comping is not fully [& conveniently] implemented in GarageBand, as it is in Logic and other DAWs -- you can either fake it with the approach I suggested, or upgrade to a real DAW [if that feature is critical to your workflow]. Command-J is really meant to join different segments of audio into one new file, but since the method of comping shown in the video seems to strip away the references to the extra data [or audio] in a multi-take Region after you cut it up, I'd guess that's why it's not going to do what you want it to -- in fact, it doesn't seem to work at all with edited multi-take recordings [MIDI or audio], so forget about it for this application..

Yes, I am forgetting about it, I mean in comping at all. I just listen to different takes I have recorded one after another, if I want to compare them - much easier. I don't understand, what means to duplicate track? There is a sentence - you can also duplicate a selected track by pressing cmd d. So what it means? If I have a classic clean with recorded regions, I can duplicate it? But why? That I'd have two instruments as, for example, a classic clean in the orchestra? Like 2 the same drums, 2 stainway pianoes in one song... ? That's the idea.. ? Or what is the sense of duplicating a track.. ?

A duplicate track is exactly that -- a track with the same instrument/plug-ins/settings as another track. Besides using duplicate tracks for alternate Takes, you could break up a recording/part into different Regions (i.e. kick drum, snare, drum, hihat, etc, all on different tracks all playing the same instrument, as one example)..

Well, but how can I duplicate? I selected track (made active) with the track name with track header also the region of the track went active. Then I hit cmd d and only the name of track with track header duplicated. The region (a real music what I need to get twice) didn't duplicate. Duplicating means, that all the track option on the trck list and all regions of the track on the timeline duplicates all together? Or how? What I did wrong? It's my first time ti duplicate a track and no succeed.. I made 2 attempts and in the second one I even activated separately a region, too (if it is needed at all?). No help...

No, when you duplicate a track [with Command-D] only the track is duplicated, not the Region[s] in it. As I described [in the step-by-step post], in this scenario you'll have to copy the Region[s] from the original track to the duplicate[s] yourself.