Enrollment
Joining, Enlistment
noun, verbal noun
If you enter a group, it's called enrollment or enlistment. You're joining the group.
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.
このチームには、入団テストを受けて合格した人だけが入団できます。
Only those who have taken and passed a tryout can join this team.
これを見てイチローのマリナーズ入団当初のシチュエーションを思い出しました。
This reminded me of Ichiro's situation when he first joined the Mariners.
その教団に入団しても、何の得にもならないよ。
You won't gain anything out of joining that religious organization.