Learn German: Wir gratulieren ihm heute. - We are congratulating him today.

The verb gratulieren (to congratulate) is a special verb in German that always requires a dative object. Even though we say "congratulate him" as a direct action in English, German treats it more like offering congratulations to someone. That is why we must use the dative pronoun ihm.

Wait, so does ihm mean "to him" here?

Exactly! While the English translation just says "him", the dative case often carries the built-in meaning of "to" or "for" someone. Thinking of this sentence as "We offer congratulations to him" will help you remember why the dative pronoun is used.

Is ihm only used for masculine words?

The dative pronoun ihm is used for both masculine ("he") and neuter ("it") nouns. Here, it most likely means "him", but depending on the context, it could also refer to a neuter noun, like das Kind (the child) or das Mädchen (the girl).

Could I change the word order and say Wir gratulieren heute ihm?

You can, but only if you want to put heavy emphasis on ihm (meaning "We are congratulating HIM today, not someone else!"). Normally, short pronouns like ihm tuck in right after the verb, before time words like heute (today).