You do not need to ‘open’ the new fiscal year as a separate activity. Once you make a posting into the new fiscal year, the new fiscal year is automatically opened. Or, the new fiscal year is automatically opened when you run the ‘balance carry-forward’ program.
However, you need to have (1) the relevant posting period already open in the new fiscal year, (2) completed the document number range assignment if you are following a year-dependent number range assignment, and (3) defined a new fiscal year variant if you follow the year-dependent fiscal year variant.