The plain SS officially the 'Allgemeine SS" was the basis for all other parts of the organisation. The Waffen SS was fomred from the Politische Bereitschaften (Political Readiness Squads) and it became the Military SS, the SS army. Members of the Waffen SS generally had to be members of the Allgemeine SS, but members of the Allgemeine SS did not have to be members of the Waffen SS. This is a very simplified explanation.