Does your planet have one culture? Several? How do you make those distinctions? What do your people celebrate? How?
Lots of questions! I’ll answer as best as I can, but that really covers a lot of ground.
There are lots and lots of cultures on Darisa, the same as on your world. Some of them are regional, but some of them are scattered all over the world, yet retain solidarity. They tend to follow language pretty closely, but I think that makes sense. You tend to communicate traditions with people who you’re able to talk to most easily. There are trends in cultures overall, but I can’t think of any absolutes that are 100% true across all of our cultures.
As for celebrations? Eesh, that’s even harder. Even within single cultures, there can be different celebrations and festivals that happen. Most countries celebrate the day that they were founded (mine’s no exception).
My parent is a member of the Siasha religion and raised me that way (which I kind of believe in a non-literal way), so I have always celebrated those holidays. My favorite has always been the festival of Sha. That takes place based on the position of the moons relative to Cikil, our sun, so it can happen more than once in a year, or not at all in s number of consecutive years. It is celebrated whenever KurDod, the smaller of the two moons, eclipses Kur, the larger, perfectly. KurDod is much smaller, so this places it in the center of a larger moon. In addition to this, the sun must be fully set, and the moons in a waning phase, so it looks like one crescent is being nestled into another.
We fry sappy leaves with spices and eat them on that holiday, which I always love doing. It’s one of those foods that people look at you funny if you eat at any other time though.