Learn German: Als ich bei der Firma angefangen habe, wurde ich nervös. - When I started at the company, I became nervous.

The word als (when) is a subordinating conjunction. This means it kicks the conjugated verb—in this case, habe—all the way to the end of its clause.

Why does the second half of the sentence start with the verb wurde instead of ich wurde?

In German, the verb in a main clause must be in the second position. The entire first clause (Als ich bei der Firma angefangen habe) acts as the first block or position. To keep the verb in position two, wurde has to come right after the comma, before the subject ich.

Both als and wenn mean "when". Why do we use als here?

We use als for single, one-time events that happened in the past (like starting a job). If you were talking about something happening in the present, or something that happened repeatedly in the past ("whenever"), you would use wenn.

Why is it bei der Firma? Isn't the word for company die Firma?

Yes, it is die Firma. However, the preposition bei always requires the dative case. In the dative case, feminine words change their "the" from die to der, making it bei der Firma.