Hello ChuNa. The FreeSurfer data is included in the Brainstorm OMEGA tutorial data to simplify going through the tutorials for the users, since producing the surfaces is not part of Brainstorm itself. However, it is not currently in OMEGA. Therefore, as stated in the anatomy tutorial:
Brainstorm cannot extract the cortex envelope from the MRI, you have to run this operation with an external program of your choice.
I've added a sentence to that effect in the Brainstorm OMEGA tutorial so that it is clearer.
Cheers,
Marc