What is storage class and what are storage variable ?

Storage class are used to define the lifetime and scope of a function or available.There are four storage classes namely auto,static,register and extern storage classes.
Storage variables are the variables which assigned to storage classes it determines the lifetime and scope.
Auto-lifetime is till the execution of program and scope is local to the function or program.
Static-lifetime is static and scope is internal to the unit for which it is created.
Register-variables are stored in faster access memory.
Extern-lifetime is static scope is global as it can be accessed anywhere in the entire program or outside a function.