Learn Farsi: من در مصاحبه اشتباه کردم.

In Farsi, 'to make a mistake' is a compound verb: اشتباه کردن (eshtebâh kardan). While kardan often translates to 'to do', these compound verbs are fixed pairs. You don't translate the English word 'made' directly; you just conjugate the kardan part, giving us اشتباه کردم (eshtebâh kardam) for 'I made a mistake'.

Where is the word for 'a' in 'a mistake'?

Farsi doesn't strictly need an indefinite article like 'a' or 'an' when using a compound verb like اشتباه کردن. The noun and verb combine to express the general action of 'mistake-making'. If you wanted to emphasize making one specific mistake, you could say یک اشتباه کردم (yek eshtebâh kardam), but it is completely natural to leave it out.

Since this lesson is about pas and banâbarin (so/therefore), how would I use them to continue this sentence?

You would place either conjunction right after this sentence to introduce the consequence of your mistake. For example: من در مصاحبه اشتباه کردم، پس کار را نگرفتم (I made a mistake in the interview, so I didn't get the job). The conjunction always sits at the start of the result clause.

Is the word مصاحبه (mosâhebe) used for all types of interviews?