Learn Farsi: او در یک نظام حزبی کار می‌کرد.

The base word here is the noun hezb (حزب), which means a political group or "party". By adding the suffix -i (ی) to the end, it becomes the relational adjective hezbi (حزبی), which means "pertaining to a party" or "party-based". Therefore, nezâm-e hezbi means a "party system".

How do we link the words for "system" and "party" together in speech?

You connect them using the ezafe vowel, pronouncing the phrase as nezâm-e hezbi. Even though this connecting -e sound is rarely written in the Farsi script, you must say it to link the noun nezâm (system) to the adjective hezbi (party-related) that describes it.

Why does the verb kâr mi-kard (کار می‌کرد) have the mi- (می) prefix if the sentence is in the past tense?

The mi- prefix isn't just for the present tense! When you attach it to a simple past tense verb like kard (he/she did), it creates the past continuous tense. In this sentence, it changes the meaning from "worked" to "was working" or "used to work", showing an ongoing or habitual action in the past.

Could we put the prefix mi- at the very beginning of the verb and say mi-kâr kard?

No, because kâr kardan (to work) is a compound verb made up of a noun (kâr, meaning work) and a "light" verb (kardan, meaning to do). Verb prefixes like mi- must attach directly to the verb portion (kard), leaving the noun half completely separate.