How to properly use Dispose in Unit Of Work Pattern?

I know this question has been asked several times before, but I couldn't get the answer I was looking for. So, I've implemented the Repository (generic) and UOW pattern, so I can access my DB using EF. Here's part of the UnitOfWork class:

    protected virtual void Dispose(bool disposing)
    {
        if (!disposed)
        {
            if (disposing)
            {
                entities.Dispose();
            }
        }
        this.disposed = true;
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

The question is: Who is calling the void Dispose method?? I've seen no example of the usage of that method.

this it the upper part of the Unit Of Work class:

    private BDEntities entities = null;

    public UnitOfWork()
    {
        if (entities == null)
        {
            entities = new BDEntities();
        }
    }

Is this right? should I use "Using"? and if yes, than why do I need the Dispose method?

Can you give me an example of a proper and simple usage?

Thank you, Rotem