difference between static function and normal function?and give Example.

In C, a static function is only visible within the same file. As far as other files are concerned it does not exists at all.
You can't give an example for that because we don't have files here!

If you meant C#, then static has a different meaning.
For C#, static means that there is a single instance of the method, which is not related to any instance of the class. You access a ststic method via teh class name, instead of via a class instance:

class MyClass
   {
   static void sm(){}
   void nm(){}
   ...
   }

MyClass instance = new MyClass();
instance.nm();  // Valid
MyClass.nm();   // Illegal - needs an instance
MyClass.sm();   // Valid

Think about cars: you can ask the question "how many wheels has a car?" because all cars have four wheels. "HowManyWheels" is a static method of the Car class.
But you can't ask "what colour is a car?" because you need to specify which car you are talking about: "what colour is my car?" or "what colour is that car?"