This is a question I hope the majority of this website explains. However, I figured I’d start off giving some general worldbuilding tips, in case you don’t know where to start.
Worldbuilding seems like a giant, insurmountable task when you think about it. You’re just one human, how can you create an entire universe in your head? Obviously, it can’t exist entirely inside our heads, we can’t remember all that information. That’s why we write down all the details. It is possible to create a pretty elaborate universe if you write all the details down, and that’s how I tend to worldbuild.
I use a wiki program to keep track of all my world’s details, and if you’re willing to put in the work, it really helps. Wikis let you link pages together that are related, and basically function like wikipedia (hence the name). If you want to look something up, you can pull it up right away. I used to put all my worldbuilding stuff in assorted Word documents, and while that worked, it was a lot messier. Wikis clean everything up and keep it organized, which is why I like them better. Some good wikis I've used are Tiddlywiki (in-browser) and Zim (a desktop program for Linux users).
Now I bet you’re saying, “I know how to organize, tell me the good stuff!” Organization is a bit boring, but it’s still important. But don’t worry, there’s definitely more to worldbuilding than that.
These are some of the main things I try to develop when I am worldbuilding:
And here are some minor things that you don’t necessarily have to develop, but they are nice and make the world have more depth:
The main points are elaborated on in the other articles on this site, if you'd like to read further. Hopefully this beginning article has given you some food for thought, and a place to start brainstorming.
Speaking of brainstorming, my favorite way to brainstorm is to dump whatever comes out of my brain into a Word document, and then extract the relevant information to put in the wiki. You never know what your brain will come up with. Good luck!