What do they mean?
While recording, when I stop recordin and restart, at the same track, every time there is a new vertical black line at the recording at two tracks. When I click over with the cursor, it disapears. Could someone explain what is the influence of that black vertical line?
Thanks a lot.
Mad
It’s a clip line - it’s intended to be there to show the different parts of your recording.
As you’ve already discovered you can remove it by clicking on it -good that means that that is “discoverable” (something we strive for) 
See this page in the Manual to read about clip lines and clips: https://manual.audacityteam.org/man/audacity_tracks_and_clips.html
I’ll think about putting some material in the Manual page(s) on recording that shows and talks about the clip lines between recording sessions.
Update: Iv’e added some editor notes in the alpha manual to remind me to do this - this has been a useful “nudge”, thank you for that.
WC
OK so I updated the Recording page in the Manual for the upcoming 2.2.1 release with an image: https://alphamanual.audacityteam.org/man/Recording#Recording_on_the_same_track
And I adding some text and links to that section containing the image:
https://alphamanual.audacityteam.org/man/Playing_and_Recording#record
https://alphamanual.audacityteam.org/man/Basic_Recording,_Editing_and_Exporting#Step_1:_Recording
This is something that we introduced in the recently released 2.2.0 version where we changed to be the default recording mode to be “Append Record” rather than “Record on new Track” and the developer who did that decided it would be a good idea to add the Clip lines. And I overlooked documenting that - so, once again, may thanks for the “nudge”. 
WC
Thanks a lot. So, it’s a tool. But do not interfere with the sound recorded, is that right? I can let them there and I will not hear nothing different, is that so?
You got it - no change to the audio - just markers (with some level of manipulation)
WC