-는 turns a verb into a noun-modifier describing something happening now, happening habitually, or generally true.

• 읽는 책 (the book I’m reading / a book that someone reads)
• 운동하는 사람 (a person who exercises)
• 지금 하는 일 (the work I’m doing now)

Important verb vs adjective difference:

• -는 is used with verbs.
• It is not used with adjectives (descriptive verbs). To describe a noun with an adjective, use -(으)ㄴ (e.g., 예쁜 사람, 맛있는 음식).

Form: attach -는 to the verb stem.