Find a classfile in your TeX-System

kpsewhich tex foils.cls

voss@maria:~> kpsewhich tex foils.cls
/usr/local/share/texmf/tex/latex/foiltex/foils.cls
voss@maria:~>

Install a new classfile

1. get the classfile from CTAN or from any mirror
   In most cases you'll get a name.ins and a name.dtx file. Save them in your local TeX source-directory, often: /usr/local/texmf/src. Any other dir which is found bei LaTeX is also possible. You can view this pathes with kpsepath tex.
2. Now run first latex name.ins which builds all files from the package. Than run latex name.dtx at least two times to build the documentation. If the doc has an index or a bibtex database, you need to run makeindex name.dtx and bibtex name.
3. Save the *.sty and additional font or definition files into an own subdir. It's a good idea to create one with the name of the package. Choose the path /usr/local/texmf/tex/latex/. The documentation files copy into /usr/local/texmf/doc/.
4. run texhash
5. Test if the file is found by tex with the kpsewhich-command (see above)

Pass different options to a documentclass

latex '\PassOptionsToClass{draft}{article} \input '