How to Explain Dependent Clause to a German?

I'm trying to help a friend with written English. I told her that I wouldn't be able to provide too much assistance in the way of grammar because I quite frankly just don't know the rules. I'm supposed to provide "real-world" practice outside of her schoolroom studies.

However, she did ask me why this sentence is grammatically correct.

"As Leo realises that he is nothing more than an instrument of a fundamentally deadly and unstoppable totalitarian regime, a crisis of conscience ensues."

You have to understand, as a German speaker, if you start a sentence with "Als,", you have to complete it with a dependent clause, which I think I did here, but I'm not comfortable enough with my understanding of it to explain it to her without feeling as I'm telling her a lot of false information.

The German word als translates as when in English, and makes better sense in your example. We then have a sentence that starts with a dependent/subordinate clause (When Leo realises that he is nothing more than an instrument of a fundamentally deadly and unstoppable totalitarian regime), and ends with an independent/main clause (a crisis of conscience ensues).