Hello,

The main exams you have to fight for getting a bank jobs are SBI, RBI, IBPS etc. The course curriculam is almost same for all these exam. The main things you have to focus on is English, Quantative aptitude, logical reasoning etc. topics. You can start from basic level and excel to high level. Start with basic books like RS aggrwal and if you wnat ro study high level you can go with CAT level books. You can easily manage 2-3 hours for this preparation.

Hello Amar, Greetings!
Well you cannot give bank exams after 12th immediately. The minimum eligibility to get a bank job is graduation.
After 12th, I would suggest that you should complete your graduation like BBA, B.Com in which you can take Banking and Finance as special subjects. Even if they are not there a normal graduation is fine. 
After becoming a graduate in Arts/Science/Commerce you can do Post Graduate Diploma in Banking or you can do MBA Finance & Banking, or MBA Banking from reputed BSchools in India. 
By doing professional courses like CA, CMA, CS, LLB, also you can join banks. For joining government banks, you will have to appear for IBPS exams after graduation.
Thank you, best of luck.