Some basic points for VARIABLE….

In php variables are casesensitive.
dollor($) sign represents that this is a variable.
So we can use it in our php code.

Like : $a //this is a variable not storing any value
$a = 1; //this store a value is 1. now we can use it

EXAMPLE:1 …..

Like : $a                       //this is a variable not storing any value
$a = 1;                           //this store a value is 1. now we can use it

EXAMPLE:2 …..

$a=1;

$b=1;

$c=$a+$b;                 // here $c is containing the value of both $a and $b

echo $c;                      // output
We can also say that every time a variable are assigned a value.The entire value of every expression is assign(copyed) to a variable.

Note : In php there are some predefined variable ($this) which we can not use as a variable. this will show the error.

EXAMPLE:
$this can not used by us as a variable.