system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: SD. SS. SA. Gestapo. Wehrmacht. Sipo. Kripo. What were they all and how do they relate to each other?

It's a broad question, but Nazi Germany had so many intelligence/military apparatuses it is hard to keep them straight. I especially don't know how they all relate to each other. Who was subordinate to whom? Did they interact with each other?
gpt
the Wehrmacht was Nazi Germany's military

The SS (=Schutzstaffel) was a paramilitary group founded to protect Hitler, but it quickly turned into one of the Nazi's most important instruments. The Waffen SS, which was under the Wehrmacht's command was a special unit that fought on the frontlines along with the Wehrmacht. 

The Gestapo (Geheime Staats Polizei = Secret State Police) was a secret police. Their task was to eliminate political enemies. Many enemies were put into concentration camps and they used torture to get information out of their victims

The SD (Sicherheitsdienst) was an intelligence agency that acted alongside the Gestapo

Sipo (Sicherheitspolizei) is a collective term for The Gestapo and the Krip

The Kripo (Kriminalpolizei) still exists and has existed before the Nazis. It's the part of the police that is tasked with fighting crime and preventing it.