Structure of a sentence with a subordinate clause goes like this:
Subordinate conjunction/Relative pronoun +Subordinate clause, Main Clause
E.g. Although it was raining, we went out to reach the station on time
Subordinate clause does not form a complete sentence and hence it will start the sentence with Subordinate conjunctions or Relative pronouns
Subordinate conjunctions: after, although, as, because, before, even if, even though, if, in order that once, provided that, rather than, since, so, that, than, though, unless, until, when, whenever, where, whereas, wherever, whether, while, why
Relative Pronouns: that, which, whichever, who, whoever, whom, whose, whosoever, whomever