Aquel (male) and Aquella (female) for singular Aquellos (male) and Aquellas (female) for plural Aquel, aquella, aquellos and aquellas are demonstrative adjectives, You use this when someone is pointing, thinking or remembering on something it's not close from the peoples are talking. For example: Do you remember that house? - ¿Recuerdas aquella casa? That book was good - Aquel libro era bueno That cars are big - Aquellos carros son grandes (The cars are far away from the peoples are talking). Ese, esa, esos and esas are used when peoples point or refer on something it's close to the other person. Este, esta, estos estas are used when peoples point or refer on something it's close to the person it's talking For example: I'm going to use two peoples (Carl and Lenny) and one book in three different situation. Whit the sentence "That book is new" First scene: The book is near to Lenny. It's on the Lenny's desk. Carl says: Ese libro es nuevo Second scene: The book is near to Carl. It's on the Carl's desk Carl says: Este libro es nuevo Third scene: The book is away to Carl and Lenny it's on other desk Lenny or Carl say: Aquel libro es nuevo.

yeah, xavi told. Aquello (a) it's use to refer something that its yours or something that is close to you. Example: aquella mochila es mía, you can translate as "This bag is mine"

Aquello (that): You must use when you want refering a something that it´s not here, that it´s there. "Aquello no funciona" Aquello is a pronoum. Aquella (that) The same as Aquello but in this case the name is femine. As pronoum Aquella esta cerrada. . But is an Adjetive too : Aquella ventana esta cerrada.