I am completely stuck on this lesson

public class ForumPost {
  private User mAuthor;
  private String mTitle;
  private String mDescription;

  public ForumPost(User author, String title, String description){
    mAuthor = author;
    mTitle = title;
    mDescription = description;

  }

  public User getAuthor() {
    return mAuthor;
  }

  public String getTitle() {
    return mTitle;
  }

  public String getDescription(){
  return mDescription;
  }
}

public class User {
  private String mFirstName;
  private String mLastName;

  public User(String firstName, String lastName) {
    mFirstName = firstName;
    mLastName = lastName;
  }

  public String getFirstName(){
  return mFirstName;
  }

  public String getLastName(){
  return mLastName;
  }
}

public class Forum {
  private String mTopic;

  public Forum(String topic){
  mTopic = topic;
  }

  public String getTopic() {
      return mTopic;
  }

  public void addPost(ForumPost post) {

      System.out.printf("New post from %s %s about %s.\n",
                         post.getAuthor().getFirstName(),
                         post.getAuthor().getLastName(),
                         post.getTitle());

  }
}

public class Example {

  public static void main(String[] args) {
    System.out.println("Starting forum example...");
    if (args.length < 2) {
       System.out.println("Gabriel Llanes");
    }
     Forum forum = new Forum("Java");
    // Take the first two elements passed args
    User author = new User("Gabriel", "Llanes");
    // Add the author, title and description
    ForumPost post = new ForumPost(author, "Java", "It feels great");
     forum.addPost(post);
  }
}