I am initiating and doing a basic penetration testing course and have come across one doubt.

For example in this URL: 
`http://webapp.thm/index.php=?page=1`

I get that I am requesting the `index.php` file in the server and I am specifying that I want to view page 1 as a value of the parameter.

But in this other URL: `http://webapp.thm/get.php?file=/etc/passwd`

I am having trouble understanding this request because I am requesting `get.php` (which is already a file) and the parameter `file` is accesing a different file `/etc/passwd`. 

My question is what does the `get.php` file contain in this case or is it a function? because it seems to me that it is function retrieving the `/etc/passwd`, but I know that it is not a function, so I am kind of confused about what the `get.php` means.

  got a picture describing it from the course:

[![enter image description here][1]][1]



  [1]: https://i.sstatic.net/wyPJ4.png