The 'Weapon-SS' was formed as a subdivision of the regular
SS corps in order to perform a wide variety of functions:
- The Death's Head Corps (Totenkopfverbände) administered the [concentration camps]?
- Regular Troops (Verfügungstruppen) served as elite troops and fought alongside with the Wehrmacht - the regular army
- Hitler's personal guard -- Leibstandarte.
Later there were SS-Freiwilligenverbände (volunteers) from several occupied countries (e.g. SS Division Nordland, formed from Norwegian, Danish and Baltic volunteers), an SS-Hitlerjugend division (enlisted ranks were volunteers from the Hitlerjugend? - Hitler Youth), an SS-Totenkopf Division (formed from concentration camps guards).
Up to 1944 service in the Waffen-SS was voluntary. Beginning in 1944 whole units were assigned to the Waffen-SS.
see also Nazi Germany/Organisations