Find the youtube embed code --
<iframe title="YouTube video player" width="480" height="390" src="https://youtube.com/embed/g9n_iQmBfvs?rel=0" frameborder="0" allowfullscreen></iframe>
Then take only the file code:
<iframe title="YouTube video player" width="480" height="390" src="https://youtube.com/embed/g9n_iQmBfvs?rel=0" frameborder="0" allowfullscreen></iframe>
and place it between the [ youtube ]g9n_iQmBfvs[ /youtube ] tags.
And whoop there it is...