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:roll: I found the solution!
Numeration is controlled by the \bibliographystyle{}
I had \bibliographystyle{plane} which numerates citations alphabetically.
What I needed was \bibliographystyle{unsrt} - numeration according to the order of referencing.
I'm very sorry to disturb the community with ...

Hello all,
I'm a new user of the TexShop. I installed JabRef for creating my bibliography file.
I put .bib file to the same folder, where my latex file is.
I cited the articles using the expression: \cite{key}
Then I:
1. typeset Latex,
2. typeset bibtex,
3. typeset latex twice.
During all steps 1-3 ...