In programming if we want to use values then we have to use data type to represent it’s base type as real, integer, character or Boolean that determines the possible values for that type. We can perform action on values of that type. The meaning of data, and way values of that can be stored.
Variable is a temporary storage area to storing value given by user or program. variable's type depend on data types followed by programming language. In PHP $ sign represent variable to storing value and work with it.
<?php $a=100; echo $a; ?>
In PHP using any variable we don't need to declaration of it, because in PHP variable get the data-type when we assign any value. In above example integer variable automatically defined after getting same type value.
Note:Variables in PHP are case sensitive so be careful when using $x or $X both are not same name of a variable.