How do I remember a lot of information and not forget it a week later?

Forgetting stuff after a week is normal if you're just passively reading and expecting it to stick on its own. You need active work, not passive consumption: right after watching a video or finishing a book, write down the main points in your own words, try explaining it to someone, create a diagram or mind map - your brain remembers what it actually processes.

And the key thing is repetition. Not after a week, but a day after you first encounter the material, then a week later, then a month later. There are tons of spaced repetition apps (like Anki or Quizlet) that automatically show you flashcards at exactly the right moment, when you're about to forget. Without repetition, even the best memory technique falls flat.

When I watch and read a lot, I used to forget almost everything too. Then I noticed: it helps if you do something with the information right away. Not just write it down, but rephrase it for yourself or explain it to someone (even if it's just a wall listening). Your brain works differently when you're not just absorbing stuff, but actually processing information through yourself.

The main thing is repetition with breaks in between. Read it, set it aside for a day or two, then recall it and go through it again. Don't cram everything in one sitting - come back to it several times. The first time information just skims the surface, the second time it starts to stick. If you look at your notes again a week later - it'll stay.

I also do this: if there's an interesting idea or technique, I try to apply it. Not just know about something, but actually try it in real life. That's when it really sticks. If I watched a video about some method - I use it in practice instead of just leaving it in my head's archive. And I don't rewatch videos in full - I jump to the moments I need when something didn't stick.