To Enter, To Go In
intransitive verb, godan verb
This vocab word has okurigana, which is the hiragana part that comes after the kanji. When a vocab's okurigana makes an "う/oo" sound (in this case, we have a る), it's often going to be a verb. So in this case, the kanji 入 is enter. The vocab 入る is to enter. We're just taking the kanji and using it in a verb!
はいる
When a vocab is a single kanji with okurigana, chances are it's going to be the kun'yomi reading, which you don't usually learn in the kanji (you usually learn the on'yomi reading). So, let's learn the kun'yomi reading for this word using its meaning. When you enter the room, what do you do? You say "Hi" (はい) to everyone to the point of absurdity. "Hi there. Oh hi Frank. Oh hi there Susan. Oh hi there lamp."
ジェニーはもうすぐインターナショナルスクールに入る。
Jenny will go to an international school soon.
マイケルは一人でカラオケに入った。
Michael went into karaoke alone.
スキーのクラブに入ったんです。
I joined the ski club.