Business portal is not yet available for GP 2013. It’s coming in March. You needed something to look forward to didn’t you? More info at Microsoft Dynamics GP 2013 Business Portal Update
Microsoft Dynamics GP 2013 Business Portal Update – Inside Microsoft Dynamics GP – Site Home – MSDN Blogs
Microsoft & the GP EcosystemGP 2013
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.