The demonstrative adjectives ez, az, ezek, azok (this, that, these, those) always require a definite article (a or az) right after them, before the noun (and before any other adjectives)
ez a busz - this bus
azok a kutyák - those dogs
az az orosz lány - that Russian girl
and so on.
It will sound even funnier when you add in postpositions and say things like azok között a kutyák között which glosses as "those-between-the-dogs-between", and seems like a pretty baroque way to say "between those dogs" - but you get used to it. Pretty soon it'll sound normal and the wrong way will sound jarring.