Accounting → Fiscal Years lists years with Open, Closed or Locked status and, expanded, their periods.
Creating
Calendar, label (up to 20), start and end dates. Twelve calendar-month periods are made automatically, from the start date's year, whatever your year looks like; a non-calendar year (July to June) gets periods that do not match it. The start date is not checked against the end date. A year that overlaps another is refused. The Persian calendar option appears only on a Persian-calendar site. If no year exists at all, the first posting creates a calendar year.
Periods and posting
An entry's date must fall in an open period; otherwise the posting is refused (automatic ones become Posting Failures). Close period is refused while the period holds draft entries.
Closing a year
Needs the close permission. It posts one entry dated the year's last day that zeroes revenue and expense balances into retained earnings (only if there is profit or loss to move), closes every period and sets the year to Closed. There is no reopen. "Locked" is shown but nothing sets it. Closing is refused while drafts remain.
Reversals into a closed period
Reversal always uses the original's date, so an entry in a closed period cannot be reversed. Correct it with a new entry in an open period.
Deleting
A year with any entry, even a draft, cannot be deleted.