Hola Shirley

I can see why there is a bit of confusing there. The translation in English used is not literal to what we say in the Spanish sentence, so when we say:

what it´s literally saying is "new items have just arrived" 

"New items" is the subject in this sentence - this is why the verb is agreeing with "they": they've just arrived

But we used a more natural translation in English for this, although a non literal one saying: we've just received new items.

I hope this clarified it.

Saludos

Inma

Hola Alejandro

In this case (the sentence Shirley mentioned in this thread) there is no passive or impersonal sentence, we're only using an alternative more natural translation where we are making the "subject" in the Spanish sentence the "object" in the Englsh sentence:

"...acaban de llegar artículos nuevos"

"...we've just received new items"

However, sometimes we use the 3rd person plural conjugation in impersonal sentences when the subject is unknown, irrelevant or obvious (not passive though, just impersonal). Here is a kwiziq lesson on that topic:

Spanish impersonal sentences using the ellos form of the verb

Saludos 

Inma