Installing LaTeX packages (sty, cls) - TexLive

See the URL.

A problem you may encounter:

[LaTeX output]
! LaTeX Error: Two \LoadClass commands.
[Type 'h']
You may only use one \LoadClass in a class file

You may be trying to do a \usepackage{class} when you should be using the package on the documentclass level e.g.

\documentclass[a4paper,11pt,titlepage,draft]{thesis}