Learn Italian: Non passargliela! La puntina rovina il raccoglitore. - Do not pass it to him! The thumbtack ruins the binder.

In Italian, the negative command for the informal 'you' (tu) is always formed by using non followed by the infinitive of the verb. So, 'don't pass' translates directly to non passare.

How exactly does gliela mean 'it to him'?

gliela is a double object pronoun. It combines the indirect object gli (to him) and the direct object la (it). When gli joins with direct object pronouns like lo or la, it adds an e to bridge them together, becoming a single word.

Why are the pronouns attached to the end of passare, and is there another way to place them?

For a negative tu command, you actually have two choices for pronoun placement! You can attach them to the end of the infinitive by dropping its final -e (creating non passargliela), or you can put them before the verb (non gliela passare). Both are perfectly correct.

Why do we use la in gliela instead of lo for 'it'?