attend
参加会议或仪式（如：婚礼、葬礼、典礼等；上学、上课、听报告等）
take part in
参加会议或群众性活动（如：运动会、体育等）
join
参加某个组织或团体（如：参军、入党、入团）join (s.b) in (doing) s.th
参加活动或比赛eg:
He attended school at the age of 6.
He often takes part in sports.
His wish is to join the army after graduation.
Tom, we'll go (out) for a picnic this weekend. Will you join us?
All the neighbours joined the sad family in finding the lost boy.