can somebody explain me what are variables case sensitive?

Answer 1

variable case sensitive mean that you can use the same Word for 2 variable like
$variable = 45;
$VariaBle = 62;
both are différents so if you test
if ($VariaBle == $variable) is false because php variables are case sensitive

Answer 2

first you should know what case sensitive means. A n a r two different things. one is a uppercase A where as another is lower case a.
php treats both as different variables so
$a=5;
and
$A=6;
are two different variables.

Answer 3

thanks