Crack of doom means the sound that hearlds the last judgement at the end of the world
You have to use repetition method . It means you should listen to a particular lesson many times and .structure of English language will go on to your subconscious deeply
Just listen and enjoy the lessons and read them many times and they automatically will go into your brain. Don't try to memorize them
So try easier courses You should understand all of the content and most of the words (not all of them, because you won't improve if you already know all of the words)
I suggest you to try (Power English) Course. It'll help you to learn English like a native English speaker.