Here is a congratulatory present for getting into school.
My father forgot to pay the enrollment fee.
Tom thought he got into Oxford, but apparently the acceptance letter was an April Fool’s joke his parents made.
You enter into a study (place). When does this happen? It happens when you get accepted into a school, aka school admission.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.