는

Turns a verb into a noun-describer

Attaches to an action verb so that the verb describes the noun that comes immediately after it, the way English uses "that/who" clauses or an -ing word: "the restaurant he vouches for", "the road you see on the left", "the food that tastes good". What it describes is happening now or is generally true. The past-tense counterpart is ㄴ/은 ("the friend who came") and the not-yet counterpart is ㄹ/을. Do not confuse it with the identical-looking topic marker 는, which attaches to nouns instead of verbs.