What is the difference between $message and $$message?

$message is a variable and $$message is a variable of another variable.

Example
$Message = “A”;
$A= “B”;

echo $message //Output:- A
echo $$message //output :-B

That is, a variable name which can be set and used dynamically.

We can echo above strings like

echo $Message.$A;

This weill print we “AB”

Note : variable’s value can be act as variable