Learn Italian: Mio nonno aveva molti dischi. - My grandfather had many records.

Aveva is the imperfetto (imperfect) tense of avere. We use the imperfect here because owning the records was a descriptive, ongoing state in the past, rather than a single event with a clear start and end. It describes how things "used to be".

Is avere a regular verb in the imperfetto tense?

Yes! Unlike its present tense, avere is completely regular in the imperfect. You just drop the -ere to get the root av-, and add the regular endings. For the "he/she" form, the ending is -eva, making aveva.

Why is it Mio nonno and not Il mio nonno? Don't possessive words usually need an article like il or la?

Usually, yes! But there is a major exception: singular family members. Because nonno (grandfather) is a singular relative, we drop the article and just say Mio nonno. If it were plural, you would need the article: i miei nonni.

Why does the plural word dischi have an "h" in it, when the singular disco doesn't?

In Italian, a "c" followed by an "o" makes a hard "k" sound (disco). However, a "c" followed by an "i" makes a soft "ch" sound (like in "cheese"). To keep the hard "k" sound for the plural, we must insert an "h". So, disco becomes dischi.