Subject + 参加 + Event/Activity
The verb 参加 (cānjiā) means 'to participate in,' 'to attend,' or 'to join.' It is followed directly by the activity or event being joined, without a preposition. For example, 参加了七场联赛 means 'participated in seven league matches.'
你要不要参加这个周末的跑步活动?
Nǐ yào bú yào cānjiā zhège zhōumò de pǎobù huódòng?
Do you want to join the running event this weekend?
他去年参加了三次志愿者活动。
Tā qùnián cānjiā le sān cì zhìyuànzhě huódòng.
He participated in volunteer activities three times last year.
我打算参加下个月的摄影比赛。
Wǒ dǎsuàn cānjiā xià ge yuè de shèyǐng bǐsài.
I plan to enter next month's photography competition.