You will have to enroll with ICAI after your class 12 and pass CPT exam.

After that you will be eligible for IPCC exam and after qualifying it you will undergo Articleship Training under practicing  CA.

Final exam is the last exam in which you can appear after Articleship training.

      CA is a correspondence course so you not need to take admission in any college for CA.

C. A. Course comprises of 4 Important Levels

1) Common Proficiency Test (CPT)
2) Integrated Professional Competence Course (IPCC)/IPCE
3) Three years Articleship/ Training under a Practicing C.A
4) C. A. Final

You can appear in CPT when you are appearing in your 12th class. 

 

Good Luck!!