question about PHP

In PHP, say i wanted to make a PHP file do operations to an HTML file. Say I want to store the data inputted from the box into a db, but i have to show PHP what i want to change, and by doing that, i name the list. In PHP would i point to the name? for example here's my tag...

and then in PHP i would do

$string=['THIS'];

is this correct, I'm not sure about web page programming, and i need some help

Also, can php understand to point at div tags in html? for example...

paragraph here

and then in php

$string=['header'];

this last question is kind of off topic, but is helpful to know. Say i wanted to change html text on a page. How would I do that?

thanks for your help

sorry tags didn't appear... first one was

input type=text name=THIS value=whatever

second one was

div id=header
p
paragraph goes here
/p
/div

I use EHCP =)

php can get values of tags from html pages.
such as:
<input type=text name=example>

php can get value of $example, in php script.

but, be careful that,
php does not output any tag automatically.

btw, to put here some tags, use & sign, then, lt; for ex.
display program filters out < sign if you write it normally.

so it's the name... not the value which PHP points to in the HTML? for example

&

<?php
$string=['name']; //name or value... which one does PHP point to is the question
?>

thanks for your help btw

I use EHCP =)

<input type=text name=email>

will be catched by php:
$email=$_GET['email'];

if, form method is GET,
use _POST if form method is post