How do you open a new 'Fiscal Year' in the system? | SAP-FICO

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