If the lesson-link and the explanation and solution have left you still lost, then I'm afraid you need more help than we can here provide. Sorry!
Please give serious thought to hiring a qualified local tutor, and setting aside a few hours a week (an hour or two a day would be best) for concentrated study sessions. By working with you face-to-face, your tutor can find the gaps in your knowledge which are preventing you from being able to learn the new material, providing individualized instruction to help you get caught up.
My best wishes to you in your studies!