[Iron_Cross]

Say I have an interface named MyInterface which contains two methods doSomething() and doSomethingElse() I would create the interface like this

public interface MyInterface{
    void doSomething();
    void doSomethingElse();
}

Then I'd use it like this

public class SomeClass implements MyInterface{
    public void doSomething(){
         // do some work
    }

    public void doSomethingElse(){
        // do some work here too
    }

    //
    // Anything else I want this class to have can go here
    //
}

Then to actually use that class I'd do something like

public class SomeOtherClass{
     public static void main(String[] args){
          // I can either use a direct instantiation like this
          SomeClass obj = new SomeClass();
          obj.doSomething();
          // When using direct instantiation I have direct access to
          // everything that class has to offer, all methods (non private)
          // all fields (non private) and so on and so forth

          // Or I can use indirect instantiaion
          MyInterface obj = new SomeClass();
          obj.doSomethingElse();
          // now I only have access to the interface methods
    }
}

Interfaces are good with multiple inheritence, abstraction, and reflection. Hope this clarifies it a bit. Oh, and you can use as many interfaces as you like, just separate them by commas.