Compiling LaTex bib source

I am writing my thesis in Latex, and I have the references in an own thesis.bib file which look as follows

@Article{xxx,
  author =       "D.A. Reinhard",
  title =        "Case Study",
  year =         "1985",
}

and I reference them in my main document as ~\cite{xxx}

When I compile then the main document with: pdflatex main.tex than it shows me question marks instead of the proper references to the bibliography. Do I also need to compile the bib source on its own? If yes, can somebody please tell me the command for Linux

Many thanks!