As in English and in Spanish there is a possibility in Italian to describe an action / event as something happening in a concrete moment. We have already said and given the reasons why there is the risk of an overuse of this possibility for English native speakers. The main reason is that in the past very rarely there is a real need for this structure because in Italian there are two tenses in the past, the passato remoto and the imperfetto and very often the imperfetto can be used instead of the construction stare + gerundio which corresponds to the English continuous form.
Only in the case that an action / event is to be described as something happening in a concrete moment, in other words if the other meanings of the imperfetto have to be excluded (for instance the function to describe action / events that occurred regularly in the past) the construction stare + gerundio is compulsory.
The fact that something is in process is not the main statement
A: Che fai?
B: Ciò che ho fatto sempre, lavoro.
A: What are you doing?
B: That' s what I have been doing always, working.
The fact that something is in process is the main statement
A: Posso disturbare un attimo?
B: No, sto lavorando.
A: Can I disturb you a moment?
B: No, I am working.
In this use of the verb stare there is no confusion with essere possible. The continuous forms, stare + gerundio, can only be formed with the verb stare.