PhP is one of the premier web development platforms widely used by many corporations. PhP has evolved in such a way that many frameworks are available to handle perfunctory web site tasks.
Yii has emerged as the best performer of available PHP development environments.
CodeIgniter is a great start for beginners.
CodeIgniter is a model, view, controller (MVC) framework for developing PhP applications.
Through it’s evolution CodeIgniter has become a premiere product for non rich internet application (RIA).
There are other frameworks however their flexibility and ease of comprehension wain when these two platforms are not the choice of development tools.