"Chúng tôi đọc tạp chí."
Translation:We read magazines.
A noun with no classifier or quantifier will typically refer to the noun group which in English is plural. Since there's nothing to quantify the noun "magazine", the sentence is actually referring to reading any magazine whether it be one or many. This also means there is no need for an article (i.e. the or a/an) in the English translation.
Note that this is unlike what lesson 1 may have taught us, but both the forms "magazines" or "the magazine" are accepted here.