Variable Variables

Question

I didn't understand the 'variable variables' topics:
there was a variable $a = "helloo";
$hello = "Hi!";
echo $a;
OUTPUT: "Hi!"

Answer 1

That is incorrect, it supposed to be
$a = "hello" ;
$hello = "Hi!" ;
echo $a;

What that happens is:
Let's look on the double $:
If $a = "hello", then:
$ $a = $ hello = $hello = "Hi!"

Understand?