This is the 5386th most frequent Korean word.
들
"들" means "fields" or "plural marker" in Korean.
Here, '들' is attached to the word '학생' (students) to indicate plurality, denoting multiple students.
학생들께서 교실에 들어왔습니다.
The students came into the classroom.
In this sentence, '들' follows '책' (book), signifying plural form to refer to multiple books in general usage.
책이들 몇 권 테이블에 놓여 있습니다.
There are a few books placed on the table.
Here, '들' is used with '새' (bird) to indicate plural, suggesting the presence of many birds flying in the sky.