This is the 845th most frequent Croatian word.
prijateljima
"Prijateljima" means "to friends" or "for friends" in English.
In this sentence, 'prijateljima' is the instrumental case of 'prijatelji', meaning 'friends', and is used to denote accompaniment.
Idem s prijateljima na večeru.
I am going to dinner with friends.
Here, 'prijateljima' is again in the instrumental case, which is used to indicate the entity with whom the action of the verb 'pričam' (am talking) is performed.
Pričam s prijateljima o planovima za vikend.
I am talking with friends about weekend plans.
In this case, 'prijateljima' is in the dative case, used here to denote the indirect object receiving the action of the verb 'pomažem' (am helping).