How can I record the books I've read and truly understand them?

The more I read, the faster I seem to forget.
I only have a vague impression of what I read.
Does anyone have better ideas or techniques
to help retain some of the essence of the books in my mind?
I'm a junior high school graduate, so I don't have much of an educational background.
But after reading for a few months,
it seems like I forget a lot.
I wonder if those who have read for many years
can really remember that much?
But reading really does help me
better understand what stage I'm at.
In this restless financial field,
it's really easy to feel anxious and uneasy,
because there is no stable source of income,
and it's impossible to have a stable income.