Hi Michael,
SCs are added in SLD.
Add a product first using the wizard in SLD, then proceed and add Software component (SC) and Software unit.
Go to technical systems in SLD and add your product to the system where you want to have it.
Once done with this you can syncronize your NWDI to reflect the new SC.
Sync your NWDS and you'll find your new SC and can add DC's. The available DC types for adding are dependent on the dependencies you specified in SLD or NWDI (they should be synced after changing dependencies)
regards
Sven