Printing to a PDF is a useful feature to have for saving receipts of online purchases or sending screenshots of webpages to friends (these aren't the only useful times to print to PDF's, but they are the only ones I can think of off the top of my head).
In OS X printing to a PDF is a as simple as:
Primo PDF. After installing Primo PDF do the following to print to a PDF:
Primo PDF is freeware and can be downloaded here.