You can refer to YouTube and various other websites like Coursera, edX, Udemy, etc.
I'm noting down a few links which might help you with the subject -
Apart from this, you can also solve R. D. Sharma & R.S. Aggarwal books on Mathematics. These books provide you with HOTS questions (Higher Order Thinking Skills) which will help you open your mind to new kinds of questions which can be asked.
Thanks and wish you all the best for your future!
First of all you have to be patient and work on basics, its ok to start slow there is nothing wrong in that.
You will have to understand the logic and not only focus on getting the work done.
Once you start loving the logic, sky is the limit, trust me.
Please do not be under pressure to be always good for competing someone, just compete with yourself and create a better version of you everyday.
To score good marks in Maths, it is very important to understand the concept and apply it to problem. This subject cannot be memorised.
The only way to improve on this subject is to practice as much as possible. Practice is the key.
You can refer to different books and online tutorials for concept and example questions on each topic.
Make a separate register for theorems, formulae and methodologies
Solve Problems yourself, Understand your syllabus, Practice papers are a good way to mentally prepare yourself for what you are going to get in the exams.
Pay attention in your classes.
Study according to your learning style. You may know that different people have different learning styles. Some people are visual learners, some people prefer sound, some need physical motion, and so on. Know how you learn best and work that into how you study.
Make note of formulas, important problems, theorems all in one place and revise it thoroughly before exams or tests.
Keep practicing and you will achieve your goal.
Try taking up mock test/exam 2-3 days before your actual test/exam with the similar test/exam environment keeping the time limit same as your test/exam.
All the best.
Practice always makes you perfect, just follow this strong line.
Hope for your best.