comprehend MVP in android by sample

i'm new in MVP in android and after read many document about it i cant find some answers, for example i pasted some snippet from simple source on github

in this source we have three directory as model, presenter and view; model folder have to interface class as :

public interface IUser {
    String getName();
    String getPasswd();
    int checkUserValidity(String name, String passwd);
}

public class UserModel implements IUser {
    String name;
    String passwd;
    public UserModel(String name, String passwd) {
        this.name = name;
        this.passwd = passwd;
    }
    @Override
    public String getName() {
        return name;
    }
    @Override
    public String getPasswd() {
        return passwd;
    }
    @Override
    public int checkUserValidity(String name, String passwd){
        if (name==null||passwd==null||!name.equals(getName())||!passwd.equals(getPasswd())){
            return -1;
        }
        return 0;
    }
}

comprehen problems:

why the programmer define two method of UserModel on other interface and then overrided into main class?

or into presenter folder we have other interface class.

whats compulsion to define methods on other interface and ovrride on main class?

public interface ILoginPresenter {
    void clear();
    void doLogin(String name, String passwd);
    void setProgressBarVisiblity(int visiblity);
    void onDestroy();
}

public class LoginPresenterCompl implements ILoginPresenter {
    ILoginView iLoginView;
    IUser user;
    Handler    handler;

    public LoginPresenterCompl(ILoginView iLoginView) {
    }

    @Override
    public void clear() {
    }

    @Override
    public void doLogin(String name, String passwd) {
    }

    @Override
    public void setProgressBarVisiblity(int visiblity){
    }

    @Override
    public void onDestroy() {
    }

    private void initUser(){
    }
}

and then in Activity how do work this method:

@Override
protected void onDestroy() {
    super.onDestroy();
    loginPresenter.onDestroy();
}

onDestroy() on loginPresenter class is empty method !!!