The first step is always the Idea.
What are you passionate about? What are some of your hobbies? What do you have that you can share with the world?
These questions help you look inward. We all have things that we are interested in. You may even be a fanatic about them. There are others like you.
You can Google (not sponsored) anything from classic cars to 80’s cartoons. Even though you may not know the person behind the site, you have a connection to the person who created the Wacky Races fan website. The information put onto the page is the same that they can tell you in person without missing a beat, the same way you know and can tell it just as well as them.
Maybe you studied Japanese wooden architecture and practiced it in your garage? The sources you got the knowledge from are just like you. When you start a website or Youtube channel and detail how you do it, you are passing on that wisdom to countless more.
If you struggle with the idea, start journaling. I recommend freewriting if you have no idea what you want to put on the page. Think about what you did that day. What were some things that made you smile?
I’m just trying to give you ideas.