Assister vs. participer
While both assister and participer can translate to to attend or to be present at in English, the main difference lies in the level of active involvement. You must choose the right word based on whether you are merely watching or actively contributing to the event.
Assister
The word assister means to attend an event as a passive observer, audience member, or spectator. You are physically present to watch or listen, but you do not actively contribute to the action. It is almost always followed by the preposition à.
J'ai assisté à une conférence fascinante sur l'histoire de l'art.
(I attended a fascinating lecture on art history.)
Nous allons assister au mariage de mon cousin ce week-end.
(We are going to attend my cousin's wedding this weekend.)
Elle doit assister à une réunion mais elle n'aura pas besoin de parler.
(She has to attend a meeting but she will not need to speak.)
Le directeur a simplement assisté à la présentation sans faire de commentaires.
(The director simply attended the presentation without making any comments.)
Des milliers de fans ont assisté au concert hier soir.
(Thousands of fans attended the concert last night.)
Participer
The word participer means to attend an event and actively take part in it. It shows that you are contributing, playing, working, or speaking rather than just watching. Like assister, it is usually followed by the preposition à.
Je dois participer à cette réunion pour présenter le nouveau budget.
(I must attend this meeting to present the new budget.)
Tous les employés sont invités à participer au séminaire de formation.
(All employees are invited to attend and take part in the training seminar.)
Elle participe à un atelier d'écriture tous les jeudis soirs.
(She attends a writing workshop every Thursday night.)
Mon frère va participer au marathon de Paris cette année.
(My brother is going to participate in the Paris marathon this year.)
Nous participons souvent aux débats communautaires de notre ville.
(We often attend and take part in our city's community debates.)
Summary
In short, use assister when you attend an event passively to watch or listen, and choose participer when you attend an event to actively join in the activities, discussions, or work.