What is PHP?
PHP can be used as server-side scripting language, including files, putting in date stamps, displaying counters all that stuff.
It also can be used as a form processor, and replace traditional CGI. It has a full range of features to support this, variables, expressions, control loops etc.
If you are familiar with perl, C, C++ or Java, you have a good start on PHP. There are lots of similarities. Naturally, there's lots to learn as well.