Explain the difference between $message and $$message?

• $message is used to store variable data. $$message can be used to store variable of a variable. Data stored in $message is fixed while data stored in $$message can be changed dynamically.
  Example:

$var1 = ‘Variable 1’
$$var1= ‘variable2’
This can be interpreted as $ Variable 1=‘variable2’;
For me to print value of both variables, I will write
$var1 $($var1)

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

$Message = "YOU";
$you= "Me";
echo $message //Output:- you
echo $$message //output :-Me

$$message allows the developer to change the name of the variable dynamically.