I don't understand the video completely. Near 01.35-01.40 minutes, he puts the intro back. How he puts it back? And after that, how he duplicates the intro, is holding down option. Well, I did so, and got another intro, but next the first one. Not to the end of all regions as shown on the video. If I tried to move it more far like on the video, I hold down again option it gives me move arrange marker, I moved, but instead of replace the second one, I got the third one... So now I have 3 intros (with all the tracks coming together with intro as on the video) on the line, but I wanted to move the first one more far place as on the video (as the first one remains just in the beginning and that duplicate one appears to the end). He says he duplicates and copies, but my option only gives me copy choice. And how do I get rid of those intros? Right click doesn't give me delete option and I don't know to do more...

There are two ways to duplicate a Region.. Select the Region and hit Copy & Paste, and the copy will be placed on the currently-selected Track at the current location of the Playback Cursor; or [easier & quicker] hold Option and drag the copied Region to the desired location. To delete a Region, simply select it and hit the Delete key. I can't really make sense of your description of what you did, but the above procedures should work with no problems..

I clicked on the intro, deleted, but it still stays white, not black as it was. Why? And you see, I have 3 intros on the line, I didn't want that. Why I have three of them, not as on the video (in the beginning and in the end)? Video is included. https://youtu.be/GEkaviT5wcs Also, you see, after deleting intro, a tall and narrow region appears. Why is it there? Doesn't intro is deleting fully? And I had one long drummer region, but now I have 3 smaller ones, and I did nothing for that (for getting multiple drummer regions). Does three intros mean three regions automatically? Video is included. https://youtu.be/c2pNWJgfFk4

If you select an Arrangement tab and hit Delete it will delete all the Regions below within the boundaries of that Arrangement tab; with the tab still selected [white] if you hit Delete again the Arrangement tab itself will be deleted. [If you have three of them then you must have created three of them].. The tall and narrow Region is just a leftover piece of a Region that you must have deleted via the Arrangement tab, as above. If you don't want it, just delete it. Remember if you move/copy an Arrangement tab it moves/copies all the Regions below it [as shown in the video].

I watched video again and got it. I deleted one drummer track, and now I have instead of it if I move a mouse there, a yellow +. Why it appears?

The yellow + is always there if you hover the cursor just after a Drummer Region -- apparently it's just a shortcut to make it quicker & easier to add a new Drummer Region [you could also right-click and select "Create Drummer Region"].

Yes, I see. I hit on + and first one came by the name verse (above is a verse of arrange track). Others came under name drummer (above are nothing, the drummer is my last track). That's not important, what name is a drummer region? Is that + only related to drummer regions, or does it exist in any other tracks, too? Can I create my own +, for example, to classic clean etc? That + is more comfortable than other ways to create regions...

Apparently you only get the + option for Drummer tracks -- for Audio or regular Instrument tracks you'd have to right-click after a Region and select "Add Audio File" or "Create Empty MIDI Region", respectively..