Just keep practising exam questions, we never used a book in Junior Cert Business Studies we only ever got handouts or did exam questions. For any answers that you are unfamiliar with taking down the sample answer from examinations.ie is usually the handiest way to go. Start off with ordinary level questions if you are really struggling at first or are only in second year yet.
Business Studies does not a require large amount of study especially if ya know a lot of basic stuff that does be going on in the economics and industries. Accounts can be quite hard to understand at first, especially the Final Accounts (and stay away from those long Ledger account questions) BUT with a lot of practice, they will become much easier. Like even if you get stressed out by doing so much accounts, just remember that you're doing all that hard work for your JC Business exam. I'd advise to go over a chapter like each night OR even week - because your exam isn't 'til June 13th (yes I know the exact date because JC Business always takes place on the Tuesday in June at this time of the month). After you look over some theory, why not test yourself? And then see how you did after. It was easier for me if somebody asked me questions or tested me whilst I did not look at the book, so I would think it's better to ask somebody to do it for you. If doing accounts, then get the exam papers out and do an exam question WITHOUT looking at your book.