Difference Between One-to-Many, Many-to-One and Many-to-Many?

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Ok so this is probably a trivial question but I’m having trouble visualizing and understanding the differences and when to use each. I’m also a little unclear as to how concepts like uni-directional and bi-directional mappings affect the one-to-many/many-to-many relationships. I’m using Hibernate right now so any explanation that’s ORM related will be helpful.

As an example let’s say I have the following set-up:

public class Person{
    private Long personId;
    private Set<Skill> skills;
    //Getters and setters
}

public class Skill{
    private Long skillId;
    private String skillName;
    //Getters and setters
}

So in this case what kind of mapping would I have? Answers to this specific example are definitely appreciated but I would also really like an overview of when to use either one-to-many and many-to-many and when to use a join table versus a join column and unidirectional versus bidirectional.

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