This audio is pretty bad. Also, it would be amazing to hear different voices. So far it's just been this woman and one other man. I'm further along into the lessons now and it's only ever the man. Different voices will help with various ways to hear the words being said.
Hello, classifiers helps to classify nouns in general regarding their type: like object (cái), fruit (quả), nationality (người), language (tiếng),etc. It doesn't imply a specific noun, so if you say : con cá ou cá it means fish in general, if you add the "demonstrative pronoun" as : này (this), kia (that), this implies one fish specific that you're talking about. Hope it helps :)