Yes, the tenses in English are very similar to those in Spanish.

The pretérito pluscuamperfecto is called the past perfect in English.  It is used to talk about a past finished action that took place before another past action. 

For example:

My friends has already eaten dinner when I arrived at their house.

Mis amigos ya habían comido la cena cuando llegué a su casa.

This page has a good explanation: http://www.englishpage.com/verbpage/pastperfect.html

Oh, right. I see now that it`s been simply a typo. Sorry.

Julia, Tony is right and so are you.

Of course the past perfect is formed with 'had', and I'm quite sure that Tony meant to say:

My friends HAD already eaten dinner when I arrived at their house.

The 'has' was just a typing error.

Let`s start with it that I agree with Tony. Past perfect is indeed pretty much the same of the pluscuamperfecto and the explanation is correct. But to my mind has eaten is present perfect and not past perfect . A past perfect form is for example : Before I came here, I had spoken to James. So I mainly disagree concerning "has" . I don`t exclude that I might be wrong but yeah that`s what I know :D.