Passer vs. se passer
The key difference between passer and se passer lies in their function: passer is an active verb indicating an action performed by a subject, while the pronominal se passer describes an event that happens or takes place.
Passer
A1This is an active verb that requires a subject performing an action. It is commonly used to mean to pass something to someone, to spend time, to go by a location, or to take an exam.
Je passe mes vacances au bord de la mer.
(I am spending my vacation by the seaside.)
Pouvez-vous me passer le sel, s'il vous plaît ?
(Can you pass me the salt, please?)
Le train pour Lyon va passer sur la voie 2.
(The train to Lyon will pass on track 2.)
Elle a passé son examen de conduite avec succès.
(She passed her driving test successfully.)
Nous sommes passés par le parc pour rentrer à la maison.
(We went through the park to get home.)
Le temps passe si vite quand on s'amuse.
(Time passes so quickly when you're having fun.)
Se passer
A2This is a pronominal verb most often meaning to happen, to occur, or to take place. The subject is usually the event itself, not a person performing an action. It can also describe how an event went, or mean to do without in the form se passer de.
Qu'est-ce qui se passe ici ?
(What is happening here?)
L'histoire du roman se passe au 19ème siècle.
(The story of the novel takes place in the 19th century.)
Comment s'est passée ta réunion ?
(How did your meeting go?)
Un accident s'est passé juste devant chez moi.
(An accident happened right in front of my house.)
Je peux me passer de sucre dans mon café.
(I can do without sugar in my coffee.)
Beaucoup de choses se sont passées depuis notre dernière rencontre.
(A lot of things have happened since we last met.)
Summary
In short, use passer when a person or thing actively performs an action like to pass, to spend time, or to go by. Use se passer when describing an event that happens or takes place, or to ask how an event went. The most common translation for se passer is to happen.