Beat it into your head until it sticks, like repeatedly. If it's a passage from a textbook read it once, read it again but define unfamiliar words, read it again, and find key terms. Usually, a textbook has them in bold or highlighted if not ask your teacher, p.s. write down any questions you have as they come to you and then give them to the teacher I find this helps.
Once again you reread the passage as you summarize. Then you reread the passage as you look at your notes to make sure you didn't miss anything, and read it again as you write down a "cheat sheet." At the end, you have read the passage 6 times if you need to reread your notes as many times as needed.
This is a marathon, not a race you can take as long as you need to.
How does one with ADHD get information to just fucking stick in their brain goddamnit I have a squiggly brain just like everyone else get in there you fuck AND STAY THERE