Can anybody tell me something more about .php?

PHP is extension name for recursion acronym Php Hypertext Preprocessor.
Or speaking in human language, PHP is Preprocessing language, like CGI (common gateway interface)...more like Python..anyway,
with PHP u can process and write data, HTML, CSS, on server side...
U can write other data structured files, like XML...or make PDF.

.php is file extension in wich u have php script witch executes on server side and gives u a result in your browser window...So with php functions u can access databases, like mysql, fetch data and reform it, and then result is going as we expect in HTML format in client browser...So php i scripting language witch is poweful like CGI, and have many functions for databases and many addons, like GD addon for working with graphic files...
also u can make PDF files with php..i think i give u some hint about php.