Learn Croatian: Nemoj mu ga davati! - Do not give it to him!

This is the main rule for negative commands in Croatian! When telling someone not to do something, you almost always use the imperfective aspect, even if it is a one-time action. So, telling someone "Don't give" requires the imperfective davati, whereas a positive command like "Give!" would use the perfective verb.

How does the word nemoj work in this sentence?

Nemoj is a helper word that means "don't" when speaking to one person informally. When you use nemoj to give a negative command, the main action verb that goes with it must be in the infinitive (the dictionary form). That is why we use davati instead of an imperative form.

Why are the pronouns mu and ga in that exact order?

Both mu (to him) and ga (it) are short, unstressed pronouns (clitics) that group together in the second position of the sentence. Croatian has a strict ordering rule for these: the dative pronoun (mu, the indirect object receiving the thing) must always come before the accusative pronoun (ga, the direct object being given).

I know ga means "him", so why does the English translation say "it"?

The pronoun ga is the short form for both masculine and neuter nouns in the accusative case. If the object you are forbidding them to give is a masculine noun (like novčanik, wallet) or a neuter noun (like pismo, letter), you replace it with ga. In English, we call inanimate objects "it", but Croatian uses the gender of the noun.