aquéllas as in that
How do I use aquéllas as in that in spanish?
The root word you are referring to is "aquel" and all of it's other derivatives, including aquellas, are there for number and gender agreement. Aquel, aquellos, aquella, aquellas.
In this case, then, "aquellas" would be the feminine plural of "that", so it would mean "those." And since it's feminine it would be something like "those houses"... "aquellas casas."
As for when to use it... Aquel is used when something is very far away. So it's: this thing right in front of me "este", that thing in near proximity to me "ese", and that thing far away from me "aquel". Someone please correct my poor grammar lesson if there are mistakes, but this is how I remember it.
Just like esas and éstas, except aqéllas are still further away. They are all feminine and plural, so only use them for pointing out feminine and plural things. For example, "¿Cuáles quieres?" "Aquéllas. En la balda de arriba."
Because aquéllas is plural, I would use it to mean "those", rather than "that". And, as MacFadden points out, it should only be used for groups of things that are ALL feminine.
Cuáles chicas te caen bien? Aquéllas.