As with English, there are a whole bunch of subordinating conjunctions in German. The most commonly used are als (when, used with the past tenses only), bevor (before), daß (that), ob (whether), solang (so long as), weil (because), and wenn (if).
A clause that begins with a subordinating conjunction is not the main, or independent, clause in a sentence -- it's a dependent clause. To show this, the word order is different in German. The conjugated verb goes to the very end of the clause. Here's an example of a sentence where the independent clause precedes the dependent one.
English: I should brush my teeth before I go to bed.
German: Ich soll mir die Zähne putzen, bevor ich ins Bett gehe.
But what if the dependent clause comes first? Remember, in German, the conjugated verb is the second element, or idea, in the sentence. So you write the whole dependent clause, add a comma, and then add the conjugated verb. The subject goes after the conjugated verb.
English: Before I go to bed, I should brush my teeth.
German: Bevor ich ins Bett gehe, soll ich mir die Zähne putzen.
As with English, if you want to add more clauses, adjust the word order according to the type of clause you're adding.