に
に
particle
location/direction/time marker
1.
destination/direction marker
Marks the destination or target of movement. Used with verbs like 行く (go), 来る (come), 帰る (return). 学校に行く (go to school).
2.
location of existence marker
Marks where something exists or is located. Used with いる/ある (to be/exist). 猫が部屋にいる (The cat is in the room).
3.
time marker
Marks specific points in time (dates, days, clock times). 三時に会いましょう (Let's meet at 3 o'clock), 月曜日に (on Monday).
4.
indirect object marker
Marks the recipient of an action—the person to/for whom something is done. 友達に本をあげた (I gave a book to my friend).
5.
purpose marker
Marks the purpose of going somewhere, when followed by 行く/来る. Often with the masu-stem of verbs. 映画を見に行く (go to see a movie).
6.
agent marker (passive/causative)
Marks the agent in passive and causative constructions. 先生に褒められた (was praised by the teacher).
に is one of the most versatile particles in Japanese with many uses. Compare with へ (direction only, more abstract) and で (location of action). Key distinction: に marks where something EXISTS (いる/ある), while で marks where an ACTION takes place (食べる, 働く, etc.). Time expressions: use に with specific times (三時に) but not with relative times (今日, 明日, 来週).