@Anastasia1990 - The Free Plan exists so that anyone can sign up for Miro and use it for free. If you are already a member of a Miro team -- free or not -- then you are already using Miro.

If you want to create your own free plan team, you would have to leave all teams that your Miro account profile is associated with at which point Miro will detect that your account profile is not a member of any team and prompt you to create a free plan team. Once you have done this, you can ask to be added back to any teams you were previously a member of (NOTE: When you leave a team, you will no longer be the owner of any boards you created and risk losing them).

Another option is to create a new Miro account using some other email address, and then add your current Miro profile as a member of that new team, and then make them a Team Amin. Now you will have a new Free Plan team on your existing Miro account profile.

@Anastasia1990 - Re:

 a strange story happened - I “invited” a friend to Miro’s board to show her what and how, she began to create other boards and after a while I saw that I was a member of her Team (we didn’t understand how it happened, it seems then she left).

You would have used the Team invite link option:

Once any Miro account holder clicks on that link, they are added to your Free Plan team and can see all of your boards, and create boards too. Because your friend was later gone from the team, she left the team.

More on the Invitation Settings here → https://help.miro.com/hc/en-us/articles/360022258119-Invitation-settings

If you ever want to show someone your Miro board, you can use the Visitors access to share a link for anyone -- no Miro account required -- to view your board.

NOTE: Only team members can edit or comment on boards in a Free Plan.