Your life as a writer involves building a lot of worlds for your characters to populate. Maybe some of these are like our own, but others may be very different. Regardless, you will need to determine the most effective way to tell your story to the reader, and a fair amount of this will involve the setting.
To build a world your characters can realistically interact with, you will need to take care to create something plausible. The world you create needs to make sense in your writing, and you will need to establish the world’s rules, then stick to them.
This also means creating a world that your character has a place in. This may mean pointing out how well she fits into her environment, or making it obvious how much she sticks out. Either way, she will be a part of this world and her actions will impact this.
All your characters will be a part of this world, and it’s important to consider how those other than your main characters fit into this dynamic. Since your character likely lives in a place that is populated by others, she will have memories that involve strong players in your story and those that may never make an appearance. They all matter, as they all help form the way your main character views the world and experiences things she comes into contact with.
It can be helpful to build this world outside of your writing, where you will be able to create things and see how they work before adding them into your story. This way, you can add in details and test things out. A lot of this may never make it into your writing, but it will help you establish the world that your story will take place, and this is important.