Can't Create Global Products or Categories


I’m trying to build a Multi-Vendor site based on this suggestions:

But I’m unable to create Global Products or Categories,

Right now, I have 2 sites on my network, with his own stores and I have enabled the Global shopping cart. Anyway, when I go to (where the site should show the global products) It doesn’t show any product and I can’t figure out how to do this.

Any help is welcome,

Thanks in advance!