A Conjunction is a word that connects various words, clauses or phrases. The primary objective of a subordinate conjunction is to provide the switch/transition between at least two notions in a sentence. The switch/transition reflects cause and effect relationships, such as relative/actual time and relative/actual place.
Foster will play outside when his homework is complete.
The second objective of a subordinate conjunction is to minimize the weight on a particular clause so the notions/ideas can be clear to the reader.
As Kim ran up the hill, she sprained her ankle.
Here is a list of some subordinate conjunctions:
in order that