Hey there!
First of all congratulations for successfully passing your 12th class!
Now that you are from science stream and want to take up BCOM..you need to understand few concepts beforehand so that it’ll be a bit easier in college! So here Accountancy and economics are the main subjects.You need to go through these subjects and understand the basics of these subjects.
Economics is a very interesting subject and you’ll find it easier and interesting when you understand the concept better.
Accoutancy is also easier and exciting.You need to keep practicing and know the concepts very well to get a grip on this subject. (.omg nothing can match the happiness you get after your balance sheet tallies!)
You will find loads of YouTube videos or books out there which will help you out!