When it comes to setting up a new area for a game, I find writing a primer to be particularly helpful. A primer is a brief overview of important topics for the area that can be shared with the players, but is mostly for myself. Because it is shared with players I keep this to publicly known information, or information that is easy to find out. The idea then is something you can reference to make sure you are keeping to your original idea for the area, and that can also intrigue and hint at potential stories for the area.
Weather & Climate
If I have a map I tend to think of weather and climate first. I do this because I already have information for it from the map. I also do it because the weather, climate, and geography of an area will feed into everything else.
How long is the day/night cycle in this area in summer? In winter? Is it wet or dry? Cold or hot? Are there periods of heavy rain and long periods of dry? You don't need to detail everything, but if a place spends half the year covered in snow it probably warrants mentioning.
Now that we know the area of the world the people live in, and what the weather is like, what kind of people does this breed? Fantasy tropes tends to make people in cold northern climates heartier, stoic, and pragmatic. This isn't by choice (you'll note these qualities also exist for people from deserts and wastelands in a lot of cases) but because since the land is unforgiving, and the weather is unforgiving, you get people that face that unforgiving adversity less as an affront and more as just a way of life.
That said, life is hard everywhere and always has its challenges. And every rule has exceptions. For now though, focus on the generalized view for the area. You can take inspiration from real world places with similar climates and geography, or you can make it up all on your own.
Architecture & Settlements
We know the weather. We know the people. Put those two things together and you can figure out how they would build their homes and settlements. Do they tend for small homes and small families that are easier to sustain? Do they have larger, more elaborate homes? How does it differ in cities as opposed to out in the country? This doesn't need to be long, just enough to give you some visuals for what your players will see. Again, you can borrow heavily from similar real world areas. There is a reason cultures in cold northern climates have angled roofs, while warmer/dryer areas have flat ones and it has to do with the weather both face and the challenges they provide.
Geographic Features & Places of Interest
What stands out as places of interest in this area? Is there a series of caves? A forest that stretches for miles and miles? A series of waterfalls? A range of mountains? What are some stories about these places? What manner of creatures or spirits do the local people believe live in them? What importance do they have?
This is where you can start seeding in story ideas for your area. You don't need a bunch, but a couple ideas or conflicting stories about an area can help give it life, get your players' imaginations running, and give you fodder for adventures, encounters, or stories to tell while the PCs are in that region.
What threats do the local NPCs know about and what do they know about them? Are they worried about bandits and raiders? Evil spirits that infect them with plague and kill their crops? What is going on that makes this place worthy of being the setting for your current game and adventures?
This is the other place to start seeding stories. Even if it is just rumors of missing livestock, ruined crops, and strange disappearances. Any one of those things is enough to get all sorts of tales being spread across an area from goblins to dragons and back again.
Use of the Primer
As I said in the beginning, I share my primers with my players but I don't require they read them. In general PCs tend to be visitors to an area. Maybe they know all of it. Maybe they know none of it. Generally though you can get a gauge of interest in the world with who is reading the primer, and what areas in specific they are latching onto. More to the point though, the primer then serves as a reference document for you while you're telling stories in the area.