make sure you have a copy of each powerpoint used in class. at my sixth form the teachers would just usually send it to us before the lesson or email it/put it on google classroom if i asked for it. in the lesson, make rough notes of what you can understand and make sure to jot down anything you don't understand. after the lesson, if possible, ask your teacher if they can go over the stuff you didn't get in the lesson. if not, during independent study, make sure you prioritise researching and learning these things. search for extra resources like videos, flashcards, diagrams, textbooks etc. everyone learns in different ways- find what works for you. then make proper, organised notes on everything from that lesson using your rough notes, the powerpoint and anything else you found online. that way you can be sure there are no holes in your knowledge that may come back to haunt you later. this can be a little time consuming but make sure to schedule this consolidation time into your free periods