The word kaana is the past-tense masculine singular third-person (he) form of the verb to-be. So you can translate it as “he was”. (And the khabr takes the same rules as with any other verb.)
So what does it mean when Allah (سبحانه وتعالى) uses kaana to describe Himself? For example, in surah Nisaa, He says:
Translation: And seek the Forgiveness of Allah; surely, Allah is Oft-forgiving, Most Merciful [Surah Nisaa, 4:106]
In the Qur’an, when Allah uses kaana, it doesn’t mean He was, and no longer is–rather, it’s used as a form of emphasis. The same way that you are certain about past events (like 9⁄11–it happened), you are certain when you use kaana. That is why translations carry such words as “verily”, “indeed”, “surely”, and so on.