Learn Polish: Ona często rozmawia z mężem. - She often talks with her husband.

The preposition z (when it means 'with' or 'along with') requires the noun that follows it to take the Instrumental case. For masculine nouns, this usually means adding the ending -em. In this specific word, the root also has a small spelling change: the ą swaps to an ę, changing mąż to męż- before the ending is added.

The translation says 'with her husband', but where is the word for 'her'?

Polish often skips possessive pronouns (like 'my', 'your', or 'her') when the meaning is obvious from the context. Since she is the subject of the sentence doing the talking, z mężem is naturally understood as 'with her own husband' unless specified otherwise.

How do I know the dictionary form of rozmawia?

The dictionary form (infinitive) is rozmawiać (to talk or to converse). It belongs to a very common, easy group of verbs where the 'he/she/it' form simply drops the final -ć from the infinitive, leaving us with rozmawia.

Could I put często at the very end of the sentence?

Yes, Polish word order is quite flexible. You could say Ona rozmawia z mężem często and it would mean the same thing. Putting często (often) right before the verb is just a very common and natural habit in Polish, much like it is in English.