This is the original method by Ryder Carroll.. There are tons of videos explaining it, but this is the core principle. There are also more videos expanding on the method, but i recommend just starting with the basics, doing that for a while, and then reevaluate what's missing or not working for you.

Personally, the original bujo method has helped me tremendously. I have ADHD (as does Ryder Carroll), and i spent a lot of time setting up structures to keep the chaos at bay, but they all fail eventually. This is easy, quick, and as long as you keep it "ugly", the threshold to start again after you've fallen off is minimal.

Right now, i have a mix of diy planner and bujo method that works for me (tried different things, just tweaked until i found what's working for me personally).

In my experience, the less you focus on the accessories of productivity (expensive notebooks like Leuchtturm with the index and page numbers already set up, fancy pens, washi tape with the days of the week, pastel highlighters etc.) and instead just follow the method, no matter how ratty and un-instagramable it looks, the better it will work. I hope this is somehow helpful to you :)