BIBTeX is run after you run LaTeX at least once, using the bibtex command:
bibtex latexfilename
The LaTeX filename should be without the .tex extension for this
command. When you run BIBTeX, you'll run it once with this command,
and then you'll need to re-run LaTeX (normally twice to get all the
references listed correctly) on your .tex file with the
command:
latex filename.tex
The command latex filename.tex is run from the command line, like the bibtex program command. Because this is a multi-stage process, you always get a warning message about 'unresolved references' the first time you add a new reference to a previously uncited work. This will disappear after the next time you run both BIBTeX and LaTeX again.