This is a post I’ve been meaning to upload for a long time. World building is an important aspect of all writing. Fantasy usually involves maps, and I’m sure we’ve all done plenty of those. It’s important to have a basic understanding of geography and climate so you don’t make a mistake and have two things together that wouldn’t be possible in the real world. We all suspend our disbelief for some things (eg the possibility of space travel, or indeed, existence of magic), but there’s only so far you can push this. Best to reserve your reader’s goodwill for the big stuff. I would recommend reading a textbook on it aimed at the primary school level – easy to understand and hopefully not too dense!
Think about aspects of your world such as landscape features, food sources, trade and technology, and resources that might become a basis for trade or war. Other aspects include political structure, spiritual framework and social class. All of these things will impact on the people who live there, will shape who they are and influence who they will become.
How your protagonist and antagonist are placed in terms of these things will determine how they act, what they say, even what values they have. And you’ve probably spotted it already – they can yield the conflict that will move your story forward and make it compelling.
Of course, there’s a trap too. I have to carefully time limit my world building phase, as it’s a really lovely way of putting off writing! How much of it you need depends on the writer, but I would argue you don’t need much to start your first draft. You can always drop the detail in later, and it’s just so satisfying seeing that word count go up, isn’t it?