The CSSBB certification requires you to not only learn and clear the examination, but also provide evidence that you have applied that knowledge to an actual project situation successfully. A project is a process improvement activity where you have managed to improve the performance using some of the techniques taught under Six Sigma. You must find a project for yourself, from your own organization or where you consult, and then work with the process owner to bring improvement in the process. Every such project should be done with the support and guidance of a senior manager/ leadership member of the organization, who obtains a benefit from the result of the project. Such a person need not be a MBB. Such a person is called the Champion or Sponsor of the project, and ASQ requires an affidavit to be signed by the Champion or Sponsor to attest to your having done the project satisfactorily.
I hope this clarifies what you need to do.