Learn Italian: Collezionavo i giocattoli, ma non li scambiavo. - I used to collect toys, but I didn't exchange them.

The imperfect tense is used to describe ongoing habits or repeated actions in the past. Translating these verbs as "I used to collect" and "I used to exchange" shows that this was a continuous hobby over a period of time, not just a single, completed event.

How do you build the "I" form for regular -are verbs in the imperfect tense?

Both collezionare (to collect) and scambiare (to exchange) are regular -are verbs. To make the io (I) form, you simply drop the -are ending from the dictionary form and add -avo. This gives you collezionavo and scambiavo.

What is the word li doing in the second half of the sentence?

li is a direct object pronoun meaning "them". It replaces i giocattoli (the toys) so we don't have to repeat the noun. Remember that in Italian, these object pronouns usually go immediately before the conjugated verb, which is why it sits right in front of scambiavo.

What is the singular form of giocattoli?

The singular is giocattolo (toy). It is a regular masculine noun ending in -o, so it simply changes to an -i to become the plural giocattoli.