This is the 4577th most frequent Korean word.
가입해
"가입해" means "join" or "sign up" in English.
Here, '가입해' derives from '가입하다', meaning 'to join', used to express joining a club or group.
나는 새로운 동아리에 가입했어.
I joined a new club.
In this case, '가입해' is part of '가입하다', which implies 'to register' as an official member in an online setting.
사이트에 회원으로 가입하세요.
Please register as a member on the site.
Here, '가입하다' is used in the context of signing up for a service or policy such as insurance.