First of all you have to prepare for CLAT and give the exam. Then, you can get admission in one of the colleges of your choice for the LLB 3/5 year programme. It depends on you, whether you can to go for B.A. with LLB or not.
Once you get your degree, you can immediately prepare for the government excams through which you can get the position of sub-judge or magistrate depending on how you perform in the exam. These exams are called PCS(J) in UP or MP or Bihar or State Judicial services like Delhi Judicial Services in Delhi. Becoming a District Judge or Sessions Judge or District & Sessions Judge is the highest position in subordinate (district) judiciary and one can reach there by working for a long period of time.
However, after LLB and 7-years of practice experience, one can directly apply to Higher Judicial Services or HJS of any state and join directly at ADJ (Additional District Judge) and in such cases, elevation to DJ position becomes easier.