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:
Wiley Technology Publishing
Wrox online library: http://wrox.books24x7.com