We all know that after we send request from your browser towards the webserver(Apache).Its an Http request.Imagine that the database is on different webserver,The way the webserver will talk to the database server?Php exists inside my Webserver although not at Database server.Any assistance will be Appreciated.I don't know it may be Cleaning soap or XML,For this reason I'm asking

It's not HTTP, Cleaning soap or XML
Its likely database's own TCP/IP-based protocol implemented in database API functions put together in PHP module loaded by PHP.

database server is really a regular daemon, "listening" for inbound TCP/IP connections. Thus, there's no difference where it placed - on a single server or remote one.

So, PHP opens link with mysql server similar to as HTTP client opens an association to HTTP server or email client opens link with POP3 or SMTP server.

Within the network, having a specialized protocol implemented through the database libraries.

The applying on the internet server produces a socket link with the database server, and transmits messages backwards and forwards utilizing a protocol produced particularly for database communications, that is unique to every different database software.

You should check this link for questions like What's PHP's MySQL Extension? What's an API? Exactly what is a Connector? Exactly what is a Driver? PHP Data Objects (PDO) and much more...
php-mysqli.overview