Use singular noun "dress" with an article "a/a/the" before it. Without an article, you need to use plural form ò the noun which is "dresses".
Dùng danh từ dạng số ít "dress" kèm với một mạo từ "a/an/the" trước nó. Khi không có mạo từ đi kèm, ta phải dùng dạng số nhiều của danh từ ấy "dresses".
Dress is a singular noun (she wears a dress) or a verb (I dress myself). Dresses is a plural noun (she has many dresses) or as the verb with the 3rd person pronoun (she dresses herself). In the example we just did on this course, dresses is used because anh ấy likes to wear many different dresses, not just one specific dress.
I might be wrong, I am not Vietnamese but my understanding is that in Vietnamese if you do not use classifiers, nor a demonstrative or a number (this, that, one) then it implies you like them all in general. Otherwise, classifiers are needed.
Tôi thích chó = I like dogs Tôi thích con chó này = I like this dog Tôi thích những con chó đó = I like these dogs