It depends upon what are you intended to do. There is
no steadfast answer where you should apply the
modifier. Whether you are a developer, programmer, or
student, you embark upon the digital language writer
career field -- be creative.

It means  that the field or method is accessible via the class. Example:


public class Thing{

public static  void staticMethod(){ }

public void instanceMethod(){ }

}


The method staticMethod() can be accessed via Thing.staticMethod() and
you don't need an object, whereas with the instanceMethod() you would
first need to create an instance of MyClass to access the method:

Thing thing = new Thing();
thing.instanceMethod();

If you declare a variable or method static  it means  that it is a class
variable or method. Then you can access it with something like

x = MyClass.staticVariable;

but if you don't declare it static you would have to use something like

MyClass obj = new MyClass;
x = obj.nonStaticVariable;

http://www.cs.umb.edu/java/keywords/static.html