Pluperfect (Past Perfect)  

This is to express you you had already done. I had gone to the store. When Carlos arrived the train had already left.  

Formula: imperfect of haber + past participle

And the past participle is formed with ido and ado endings. (See Present Perfect)

This construction is usually used with the preterite. (See Preterite)

This summer we went to Spain. We had never been abroad before.

Este verano fuimos a España. Nunca antes habíamos ido al estranjero.

El altoparlante anunció que el avión de Quito había llegado.

The loudspeaker announced that the plane from Quito had arrived.

I had never flown in a plane before.

Nunca antes yo había volado en avión.

When Mr. Martinez arrived at the airport, the plane had already left.

Cuando el Señor Martinez llegó al aeropuerto, el avión ya había salido.