• What is a PHP File?
• What Can PHP Do?
• What's new in PHP 7
• References

• PHP is an acronym for "PHP: Hypertext Preprocessor"
• PHP is a widely-used, open source scripting language
• PHP scripts are executed on the server
• PHP is free to download and use

• PHP files can contain text, HTML, CSS, JavaScript, and PHP code
• PHP code is executed on the server, and the result is returned to the browser as plain HTML
• PHP files have extension ".php"

• PHP can generate dynamic page content
• PHP can create, open, read, write, delete, and close files on the server
• PHP can collect form data
• PHP can send and receive cookies
• PHP can add, delete, modify data in your database
• PHP can be used to control user-access
• PHP can encrypt data

• PHP 7 is much faster than the previous popular stable release (PHP 5.6)
• PHP 7 has improved Error Handling
• PHP 7 supports stricter Type Declarations for function arguments
• PHP 7 supports new operators (like the spaceship operator: <=>)

more info in w3school.