Hello Priyanshi,

If your basics are weak, I'll suggest you to study a crash course and basics of economics and accounts on YouTube and you can refer to notes online available for more help.

That will be enough for you to get along with your 12th examination.you need to focus more on the syllabus of 12th to secure good marks which may help you in getting good colleges.

Later According to the syllabus of entrance examinations you can also learn what you didn't studied or you don't know much to score well in your entrance examinations.

I hope it helps,

Best of luck.