What is PHP?
First of all i need to say that PHP is a language which you are going to in love with. (That is of course if you are a developer ) PHP stands for PHP: Hypertext Processsor.
To start with it you should have knowledge about basic scripting and HTML language.
PHP is totaly free to use and download that is because it is an open source. Well there are many scripting languages on the earth. PHP is server-side scripting language. It means codes are executing on the server-side not in the client-side.
Thus, clients cannot see your php script, a client can only see pure html content. Now i can say PHP is secure langauge since user cannot see your PHP code. How it works? For instance, a client (user) requests a webpage from your server. Then your server executes php code and returns pure html content to the user. And user have no chance to see what is going on at the server-side.
Extensions : .php, .php3, .phtml
It works efficiently on server-side. PHP language supports many database programs such as MySQL, ISS, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc. And yes it is cross-platform. It runs on many-platforms MacOS, Windows, Linux, Unix, etc. and compatible with almost all servers.
I will keep writing on PHP topic with more details.