Let’s take a look at the plural marker 들 and how it’s used. The first sentence we’ll take a look at is, 사람들이 많아요. (사람 = person. 들 = plural marker. 이 = subject marking particle. 많아요 = many). Let’s compare this with a second sentence, 사람이 많아요. The difference between the first sentence and the second sentence is that the first sentence has the plural marker 들 and the second sentence lacks the plural marker 들. Just one particle changes the meaning of the sentence. The first sentence that has the plural marker 들 means, “There are a lot of people”. The second sentence without the 들 means “There is a person.”

One other thing that you should keep note is that just because the plural marker is attached doesn’t mean the subject marker disappears. Notice in the first sentence the subject marker comes after the plural marker. Now sometimes 들 can be dropped when it’s clear that the subject is plural. For example, 저희는 학생이 아니에요. (저희 = we. 는 = topic marking particle. 학생 = student. 이 = subject marking particle. 들 = plural marker. 아니에요 = is not.) This sentence means, “We are not students.” This sentence would also be correct if it had the plural marker 들 after the pronoun 저희. Since 저희 means “we”, it is already plural in nature. That’s why it’s ok to drop the 들.

Now let’s look at some pronouns and see if the meaning changes when 들 is added.

저희 = we. 저희들 = also means we.

너희 = you plural casual. 너희들 = you plural casual.

당신 = you singular polite. 당신들 = you plural polite.

그녀 = literally means “that girl”. 그녀들 = those girls.

그들 = can mean “they” as in a mix of boys and girls or just boys.