Learn Polish: Mamy wreszcie zgodę, więc chcę zaprzyjaźnić się z twoim bratem. - We finally have an agreement, so I want to become friends with your brother.

The verb zaprzyjaźnić się means "to become friends." In Polish, verbs about relationships and interacting with others are often reciprocal, meaning the action goes both ways. These verbs use się alongside the preposition z (with) to show who you are interacting with.

Why is it z twoim bratem and not z twój brat?

When the preposition z means "with" (as in accompanying or doing something with someone), it requires the noun and its adjectives to be in the Instrumental case. The basic phrase twój brat (your brother) changes to twoim bratem in the Instrumental.

Why is the word for agreement spelled zgodę instead of zgoda?

It is the direct object of the verb mamy (we have). The dictionary form is the feminine noun zgoda, but direct objects generally take the Accusative case. For feminine nouns ending in -a, this case changes the ending to -ę.

What is the difference between zaprzyjaźnić się and przyjaźnić się?

Przyjaźnić się is an imperfective verb meaning "to be friends" (an ongoing state). Zaprzyjaźnić się is the perfective version, which means "to become friends" or "to make friends" (a completed action). Because the speaker wants to start a new friendship, they use the perfective form here.