ACA - Associate Chartered Accountant
FCA - Fellow Chartered Accountant
The one who passes CA final both groups and gets registered himself/herself with the ICAI becomes ACA from the date of registration as a member.
An ACA becomes FCA on completing 5 years of practice but only if he/she applies for FCA. It is implied here that an ACA can practice only after obtaining COP (Certificate of Practice) from the ICAI.