Webmasters learned a long time ago that HTML alone cannot produce enticing and lasting Web sites. Thats why server-side technologies such as CGI scripts have gained widespread popularity. With them, Web page designers can create dynamically generated Web applications. Often database-driven, these advanced sites require less manual work to update and maintain than static HTML pages, and they allow for e-commerce and other advanced transactions. PHP lets you exponentially expand what you can do with the World Wide Web.
The advantage PHP has over basic HTML is that the latter is limited and one-sided. Visitors to HTML-only sites see simple pages that arent customized for them and dont display any dynamic behavior. With PHP, you can create exciting and original documents based on many factors--the time of day or whether the user is a repeat visitor, for example. PHP can also interact with databases and files, handle email, and do many other things that HTML cannot.
But the question remains: Why should a Web designer use PHP to make a dynamic Web site instead of CGI (Common Gateway Interface), ASP (Active Server Pages), or JSP (Java Server Pages)?
First, PHP is both faster to program in and faster to execute than CGI scripts. I wont get into too much detail, but suffice it to say that compared to full programming languages like Java, C, or Perl, PHP is much easier to learn and use. People--perhaps like you--without any formal programming training can write PHP scripts with ease after reading a book like PHP for the World Wide Web: Visual QuickStart Guide. In comparison, ASP requires an understanding of VBScript, and CGI requires Perl (or C), both of which are more difficult to learn, not to mention presumably more expensive to develop in.
Second, PHP was written specifically for dynamic Web-page creation, whereas Perl (and VBScript and Java) were not, inferring that, by its very intent, PHP can perform certain tasks faster and easier than its alternatives.
My final argument for learning PHP is that, once you do, and as its popularity continues to grow (it is already being used on nearly six million Web sites), you will find yourself well ahead of the learning curve on this, the latest next big thing in the world of Internet technology.