Hibernate annotation. How to annotate?

I am making a small library project in Java EE. I have created 3 tables and class with authors, genres and books. Now I am trying to connect it using hibernate, but i haven't ide how confire annotations ... Please help me :)

bookTable:

| id_book | author_id | title | genre_id | description | photo |

genreTable:

| genre_id | genre |

authorTable:

| author_id | author|

It is easy structure:

bookTable.author_id - authorTable.author_id = ManyToMany

bookTable.genre_id - genreTable.genre_id = OneToOne

Below there are my pojo class:

@Entity
@Table(name = "books")
public class Book implements Serializable{

    private static final long serialVersionUID = -5057364006691079475L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "user_id")
    private Integer user_id;
    private Author author;
    private String description;
    private BookGenre genre;
    private String title;


    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public Integer getUser_id() {
        return user_id;
    }

    public void setUser_id(Integer user_id) {
        this.user_id = user_id;
    }

    public Author getAuthor() {
        return author;
    }

    public void setAuthor(Author author) {
        this.author = author;
    }

    public BookGenre getGenre() {
        return genre;
    }

    public void setGenre(BookGenre genre) {
        this.genre = genre;
    }

}

@Entity
@Table(name = "author")
public class Author implements Serializable{

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "author_id")
    private Integer author_id;

    @Column(name = "author")
    private String author;  

    public Integer getAuthor_id() {
        return author_id;
    }

    public void setAuthor_id(Integer author_id) {
        this.author_id = author_id;
    }

    public String getAuthor() {
        return author;
    }

    public void setAuthor(String author) {
        this.author = author;
    }
}

@Entity
@Table(name = "genre")
public class BookGenre implements Serializable{

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "genre_id")
    private Integer genreId;

    @Column(name = "genre")
    private String genre;


    public Integer getGenreId() {
        return genreId;
    }
    public void setGenreId(Integer genreId) {
        this.genreId = genreId;
    }
    public String getGenre() {
        return genre;
    }
    public void setGenre(String genre) {
        this.genre = genre;
    }

}