php

as a demonstration (and test):

create a web hosting account
create a home page
add to it a log-on or log-in

once logged in you get to add, remove, and move images

i'm gonna say there's one kind of file that's required to make this happen
php
i would write some php
put it in files at my domain, my web hosting account
and
that's it

index.php would do certain things when called
what are they?
how do i define that?