Question

On a website I’m making, I would like to know how a user landed on a particular page (say here.php). There could be two possible ways: by clicking the link on page1.php or the link on page2.php. How can I find out how the user reached, so that I can provide content according to that.

Answer 1

HTTP_REFERER

$_SERVER['HTTP_REFERER'] ^DOCs should give you page the user has arrived from:

The address of the page (if any) which referred the user agent to the
current page. This is set by the user agent. Not all user agents will
set this, and some provide the ability to modify HTTP_REFERER as a
feature. In short, it cannot really be trusted.

Using a session

If you want to track a users progress through your site then it would be easier/safer to set a session (session_start() ^DOCs) and use that to track them as they land on your pages.