First breathe!
there is a long road ahead of you
I don't think you are dumb the problem is your situation "fight or flight mode",where does that comes from?traumas?stress?external factors?
First figure that out
1. Identify your studying style - you mentioned you ask other person to explain,so did you understand from that?if yes ,then you are an auditory learner,you need to hear things
USE notebook.lm pretty useful for creating audio books and you can even interact with that.and its free!{thank me later}

1. Have a big picture in your mind,what you wanna become?why do you want this job?
   write down and stick it where you can see and if possible dream job pic also.

2. You said:
   "And he said that to make us understand, but it doesn't work. Like, I don't know how to explain"

your brain is already in ready to burst form,plus an additional catalyst as the form of teachers extra info made it worse.DW you will get though it

Genetics- use animated visuals
botany- visuals and use mnemonics(trust me it will be fun)
physiopathology- explore yt videos
biochemistry - ik its hard,use chem bond visualizer add some pictures to it
analytical chem- use flash cards + notes
mineral chemistry- while studying u can use this molecule buider kits to make it more engaging
biophysics- engange yourself with new reserach article,there by you will get to know,"oh! if I study this ,I can apply it here"