Learn Italian: Avevo un bel diario e ci ho scritto una canzone. - I had a nice diary and I wrote a song in it.

Avevo is the imperfect tense (imperfetto) of avere. We use it here because having the diary was an ongoing state or situation in the past, rather than a single, sudden event. When you describe what you owned, how you felt, or how things were in the past, the imperfetto is the right choice.

Why does the sentence use ho scritto instead of the imperfect tense like avevo?

This sentence is a perfect example of how Italian mixes its two main past tenses. Avevo sets the background scene (you possessed a diary). Ho scritto (I wrote) is the specific, completed action you took against that background. You finished writing the song, so it takes the passato prossimo.

What does the word ci do in this sentence?

In this context, ci means "in it." While you might already know ci as "us" or "there," it is frequently used to replace a location phrase starting with in, a, or su (on). Instead of repeating "in the diary" (nel diario), we just put ci before the verb.

Why is it un bel diario and not un bello diario?