Learn Italian: Scusa, ho perso il tuo libro! Non importa. - Sorry, I lost your book! It doesn't matter.

Perso is the irregular past participle of the verb perdere (to lose). While a regular form (perduto) exists, perso is much more common. Like most transitive verbs (verbs that take a direct object, like il tuo libro), it uses the auxiliary verb avere.

Why do we need the word il before tuo libro?

In Italian, possessive adjectives like tuo (your) almost always require a definite article (il, la, i, or le) in front of them. You are literally saying 'the your book'. The main exception is with singular close family members, where the article is dropped.

Is scusa used for all apologies?

Scusa is the informal imperative form, used with people you would address as tu. If you were speaking to someone formally (using Lei), such as a boss or a stranger, you would use the formal version: Scusi.

How does Non importa translate to 'It doesn't matter'?

The verb importare means 'to matter' or 'to be important'. Used in the third-person singular, non importa literally means 'it does not matter.' It is the standard way to wave off an apology and tell someone not to worry.