# Bibliography doesn't work -> missing item

My bibliography of my tex document doesn't work and I can't find out why. I created 2 books in bibTex, but if I refer to them via

 %%% Main Document
\bibliography{Seminar}
\begin{thebibliography}
\bibitem[Knuth98]{ComProgram} \emph{The Art of Computer Programming}
\end{thebibliography}


The compiler says missing item on these lines. I did it just as in the tutorial in which I found these lines. The bib file is also in the same folder as the document. I found many tutorials on google but I just don't seem to get it.

The problem is the missing argument to thebibliography, which specifies the widest label:
\begin{thebibliography}{Knuth98}

Note. If you are using directly the thebibliography environment, the \bibliography command is useless.