If you are on Debian or any derived distribution like Ubuntu, it is a little harder to find out which Debian package contains your LaTeX package.
Say you want to install the Debian package that provides the LaTeX package
siunitx. Use the
apt-file program to search for the corresponding
$ apt-file search siunitx.sty texlive-science: /usr/share/texlive/texmf-dist/tex/latex/siunitx/siunitx.sty
Then install that package:
# aptitude install texlive-science