First you make a regular HTML form page, like we learnt here:
 

<form action="form.php" method="post"> Your name: <input type="text" name="name"><br> Your age: <input type="text" name="age"><br> <input type="submit"> </form>

This form consists of two text boxes, one which is called "name" and another which is called "age". These names are our variables. We save this file as "form.html", but notice on the first line how the form points to a file called "form.php"? Well, that is a seperate file, consisting of this PHP code:
 

Hi <?php print $name; ?>. You are <?php print $age; ?> years old.

Other Basics

Other basics include if statments:

if ($x==1) { // if x equals 1 then run this :o }

and while:

while ($x==1) { // while x is still equal to 1 , run! }

Will run forever - as $x is always 1!
 

One more for now, for:

for ($i=0;$i<100;$i++) { print "We are $i<br>"; }

Will print "We are " then the nth time its dont it (minus 1 cus it starts from 0) like: