Ciao,

I think you probably would better understand using also teh articoloto determinativo example.

This question wants to know about the identity of Mario.

Mario chi è? - è un attore (he's an actor - generic)

                 - è l'attore (he's the actor - referring to a particular one, maybe the best one)

This question wants to know about the job position of Mario.                

Mario che fa? - fa l'attore 

in this case you can immagine a more structured question like

Che ruolo professionale ricopre Mario? è attore.

The difference is between what you are interested in: his personal identity (job, dreams, habit ... ) or his specific job position. I hope to have been of any help. When you read a book be carefull of which verb or preposition the author uses, it makes the difference in its meaning.

I know that as a Russian native speaker you can have this kind of problems :S If I'm not wrong, you don't use the articles!

"Marco è un attore" means obviously "Marco is an actor".

"Mario è attore" is quite informal... in proper Italian I would say "Marco fa l'attore" (if you want to say that he works as an actor)

Sono stato chiaro? ;)

thanks a lot, Silvia and Gaetano!.....yes, Alberto - there are no articles in Russian, articles are a real pain in the neck (am not sure if I can use this phrase about articles, but anyway)..thanks for the help once again

Hi

Happen to do confusion about this difference between : Marco è attore and Marco è un attore.

Somentimes we use the noun "ACTOR" to indicate the person that is protagonist of that film;

Marco is actor or Marco is the main protagonist of it.

Instead if you want to indicate Marco is an actor, it means that Marco makes as job the actor.