「入る」 (hairu) means "to enter" or "to go into" a place. This is an intransitive verb. When you use it, you generally attach the particle "に" to the noun representing the place you are entering. For instance, entering a room or a building.

「入(い)る」は、場所(ばしょ)の中(なか)へ行(い)く動詞(どうし)です。「部屋(へや)に 入(い)る」のように使(つか)います。