By teaching others you strengthen your own knowledge. Teaching helps you discover weaknesses in your own understanding so you could improve it. This will also make you learn new things or revisit the old nodes. Moreover, since everybody has unique experience and knowledge, one person's understanding of ideas might be different from others', so they can explain it in a completely different way that will be easy to understand for certain people.
The best way to learn is to teach.
Someone could say that you are not an expert, so you can't teach. But what makes you an expert? I believe everyone can be a teacher. You don't need a degree or 12 years of work experience in order to teach someone. You just need to know something that someone else wants to know. Education can be as large as the whole university course on mathematics and as small as a tweet teaching you how to make screenshots on your computer.
Pick a topic: either something you have expertise in or just something you learned recently — and make a small plan of what someone who is not familiar with that should learn it. Then using that plan design the content. It could be any medium: a post in a blog, a Twitter thread, a downloadable PDF, a video or even a whole course on the topic.
It doesn't matter the material on that topic already exists, however it would be better to find a specific niche where there is not a lot of content but a lot of people are searching for it. Keep that in mind while making your content, however this process is often done after the content is created — it's called SEO.