Popular web applications forward information to and from the server using synchronised requests. It means you fill out a form, hit submit, and get conducted to a new page with new information from the server.
Update a web page without reloading the page
Request data from a server - after the page has loaded
Receive data from a server - after the page has loaded
Send data to a server - in the background.
PHP scripts can only be interpreted on a server that has PHP installed.
The client computers accessing the PHP scripts require a web browser only.
PHP code may be embedded into HTML code, or it can be used in combination with various web template systems, web content management system and web frameworks.