Hi,

To score well in class 12th, one needs to understand the topics instead of just memorizing it. I can understand your doubt, as you are not able to understand your school teacher lectures and they also do not provide any extra classes for revision, so you feel helpless. In this case, I suggest you to increase your self study durations and try to find why in every topic instead of just what. Many students makes mistakes in this and they lose there important marks in Board examination. Make your own personal notes. You can also discuss topics with your good friends. If still you feel doubts, you can reach your class  teacher explaining your problem and will definitely help you to find resolution and give you the right direction.

You can also watch YouTube lectures that explains the topic with illustrations instead of just words or in person. It will help you greatly to understand the topics.

Thank you!