Hi Aryan18,
It sounds like you're just starting out. Is that true? Have you done any studying so far? The online question bank that is available with the OG is a decent additional resource, but it's not something that you "need" for your studies.
If you're just beginning, then it would be a good idea to take a FULL-LENGTH practice CAT Test; you can access 2 for free from
www.mba.com (and they come with some additional practice materials). If you want to do a bit of practice first, so that you can familiarize yourself with the general content and question types first, then that's fine - but you shouldn't wait too long to take that initial CAT. A FULL CAT takes about 3.5 hours to complete, so make sure that you've set aside enough time to take it in one sitting. Once you have your Score, you should report back here and we can discuss the results and any adjustments that you might want to make to your study plan.
I'd like to know a bit more about your timeline and goals:
1) What is your goal score?
2) When are you planning to take the GMAT?
3) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich