I will give you a guide which will not only help you to understand German conjunctions, subjunctions, and conjunctional adverbs but also use them correctly with the help of dozens of exercises.
You will get the system behind the German sentence structure
and I will show you which connectors use a comma and which don't.
The ebook comes of course again as a PDF file that you can easily print out and all exercises come with an answer key, so that you can check if your answer is correct.