La matinée s'est..... Why the 's' ?

Hello Renate, Here the verb is "se passer", which is reflexive verb meaning to take place, or to happen, to occur. It's a bit more unclear here because not only is it in passé composé (past tense) "s'est passé" but you also have the adverb "bien" thrown into the mix too "s'est bien passé" Think of it as "the morning went really well." I don't know at what level you are with your French, but anytime you see "reflexive" in a lesson title it refers to and explains constructions like this. There's also a good introduction found under reflexive pronouns in the glossary.

It's a little bit harder to find that glossary article that I mentioned than I thought. Here's the link: https://french.kwiziq.com/my-languages/french/glossary/134

Of course. Yes I'm familiar with reflexive verbs. I should have made the connection. Thanks.