SSL is Secure Sockets Layer, an encryption method. You'll want to read a book like Professional LAMP: Linux, Apache, MySQL, and PHP5 Web Development (
http://www.wrox.com/WileyCDA/WroxTit...76459723X.html) which discusses both Apache and PHP to see how to implement Mod_ssl in Apache.
That's covered in Chapter 6 "Apache Tricks" so you can purchase the complete Professional LAMP book or you can just purchase chapter 6 as a PDF download from Wrox Chapters on Demand:
http://www.wrox.com/WileyCDA/WroxTit..._chapters.html
Jim Minatel
Acquisitions Director
Wiley Technology Publishing
WROX Press
Blog:
http://wroxblog.typepad.com/
Wrox online library:
http://wrox.books24x7.com