Why,where and What for php is used?

Question

I am not understanding why and where php is usef

Answer 1

PHP is a server-side language and is useful for manipulating data which is stored in a database.
basically, you can make a login/logout.

Answer 2

php would send info to sql, ram. php is not the database. it's also not the only purpose it can serve; it can generate pages and do other programming tasks, divorced from any single page.

Answer 3

Do mysql and php are for same purpose