LaTeX Issue with biblography

Question

I'm very new to LaTeX so i know very little about it, please keep this in mind. So I've just written a document and I did the bibliography using the following method.

\begin{thebibliography}{}
    \bibitem{label}
\end{thebibliography}

However, I was told I needed to use Harvard style referencing and was subsequently recommended that I make use of bib files. So I created a bib file with my bibliography information. However, I can't seem to get it to work at all I've tried various resources to no avail.

How do I use a bib files within LaTeX for my bibliography (in Harvard style)?

Output currently when I implement the bib file.

Process started: bibtex.exe "Project"

This is BibTeX, Version 0.99d (TeX Live 2019/W32TeX)
The top-level auxiliary file: Project.aux
I found no \citation commands---while reading file Project.aux
I found no \bibdata command---while reading file Project.aux
I found no \bibstyle command---while reading file Project.aux
(There were 3 error messages)

Process exited with error(s)



Process started: pdflatex.exe -synctex=1 -interaction=nonstopmode "Project".tex

Process exited normally

Here is a sample from my bib file:

@book{codebreakers3,
    author = {Kahn,D.},
    title = {The Codebreakers: the story of secret writing },
    year = {1996},
    publisher = {Scribner},
    isbn = {0684831309},
    page ={235},

}

@book{Cryptonetwork,
    title={Cryptography and Network Security: Principles and Practice, Global Edition},
    author={Stallings, W.},
    isbn={9781292158587},
    year={2016},
    pages = {314,451},
    publisher={Pearson Education},
}

@article{diffie,
    author = {  W. Diffie. and  M. Hellman.},
    title = {New directions in cryptography},
    journaltitle = {IEEE Transactions on Information Theory},
    year = {1976},
    volume = {22},
    issue = {6},
    month = {November},
    pages = {644-654},
    publisher = {IEEE Press Piscataway, NJ, USA },
    issn = {0018-9448},
}

Answer 1

Depending on how you write your LaTeX documents it might be more or less complex for you to make proper use of bib files as you will need to use bibtex or biber as part of the compilation progress.

An MWE could look like the following:

example.bib

@book{example,
    author = {Example Author},
    title = {Example Book},
    year = {2018}
}

example.tex (to be compiled with biber)

\documentclass{article}
\usepackage[style=authoryear-comp]{biblatex}
\addbibresource{example.bib}

\begin{document}
    Here is some text with a reference. \parencite[Pages 1-4]{example}

    \printbibliography
\end{document}

example.tex (to be compiled with bibtex)

\documentclass{article}

\usepackage{natbib}
\setcitestyle{authoryear,open={(},close={)}}

\begin{document}
    Here is some text with a reference. 

    \cite{example} or \citep{example}

    \bibliographystyle{abbrvnat}
    \bibliography{example}
\end{document}

You probably want to check with your source/professor what kind of Harvard style he expects. While the general idea might be clear there can be some surprises like requiring a strict format for your bibliography.