variable declarations difference

First declaration is static. This is just one physical object in the whole application domain.
If it is declared in some class; and the class has many instances, this field will be only one, accessible from any instance of a class itself. Same thing about structure.

Second declaration can mean different things. If can be a local variable, then it only exist on stack, accessible only withing the method where the variable is declared.

It also can mean instance variable of the class or a structure. If you created two instances of the same class or structure, there will be two different physical instances of Number. One instance can have Number==2, another one — Number==132, for example.

Let's see:

class MyClass {
    internal MyClass(int number) {
        this.Number = number;
        StaticNumber = number * 2;
    }
    int Number;
    internal static int StaticNumber;
}
MyClass first = new MyClass(1);
MyClass copy = first;
MyClass second = new MyClass(2);

//now copy.Number == 1, because class is reference type
//first.Number == 1;
//second.Number == 2;
//MyClass.Number == 4, because it was done so by the last assignment

For future: please read C# manual before asking questions like that (and also — before programming :-) ). There is no sense to try before you learn such most basic things.

—SA