Subordinating conjunctions are words or phrases that link a subordinate (dependent) clause to a main (independent) clause.
They include although and because.
A subordinate clause (also known as a dependent clause) has two main characteristics
In order to join dependent and independent clauses together, a subordinating conjunction is required.
Example:
Whales give birth to live young as they are mammals.
or
As they are mammals, whales give birth to live young.