PostScript is a page-description language: It tells a computer or a printer how to make marks on a page, in this case to make the pages of my course notes.
The original documents are written in a technical typesetting system called TeX. It was designed for producing typeset documents, particularly those with lots of technical stuff like math symbols. The TeX file is compiled by TeX to produce a DVI (Device Independent) file. The DVI file in turn is sent to dvips, a PostScript driver, which produces a PostScript file as output.
(That is why these handouts aren't available in (e.g.) Microsoft Word format (or GIF, or BMP, or ...). I don't write them like that, and there's no easy way to do the conversion.)
I chose PostScript a long time ago because it's portable, it's a vector format (rather than a bitmap format), and it makes it easy to include pictures in my documents. PostScript has been a standard for many years; it has been largely supplanted by PDF for high-quality output.
Eventually, I hope to convert all my online notes to web pages with PDF files for printing.
The easiest way to view or print PostScript files is to use Ghostscript (a free PostScript interpreter) and Ghostview (a free GUI for Ghostscript).
If you want to obtain the software, you can find the packages at the official Ghostscript Web site.
Note:As with the notes themselves, you're on your own as far as obtaining, installing, and running these programs goes.
Bruce Ikenaga's Home Page