$name and $$name both are variables but with a single difference that is $name is just a normal php variable where as $$name is known as reference variable. It allow you to use $name variable's value as a variable for getting $$name variable value.
$name = 'Roshan'; $$name = 'Singh'; echo $name . "<br>"; echo $$name . "<br>"; // value of "$name" variable echo $Roshan //output Roshan Singh Singh // This is value of "$Roshan" variable