What is the use of static class?

I was wonder before why we need to make some  classes  as static.The reason is very simple.You can make use of its member without instantiating the object of that class.For example
public static class   Name()
{
     Name()
      {}
     public static string PersonNames()
      {
         //do some stuff here
         return stringObject;

       }
}

If you want to access the PersonNames() method in another class ,you don't need to do much.Just className.methodname();
ie.
public class CitizenDetails()
{
 Name.PersonNames();
//do further stuff
}