The year is broken into periods. You normally have 12 periods in your financial year, each one corresponding to a calendar month. However MoneyWorks lets you have anywhere from two to fifteen periods.
MoneyWorks Manual, Page 10 — Periods
If your financial year starts from January and ends in December, based on 12 financial periods, January is Period 1 and December is Period 12. If you have opted for 13 periods, that is "Twelve Calendar Months Plus End", an additional Period 13, which is also December month will be added for audit adjustment.
If you have registered your company in October 2015 and decided to close the financial year as at December 2015 (3 months), you should set your financial year from January to December. Although, there won't have any data from January to September (Period 1 to Period 9), it still considers as one financial year and MoneyWorks will carry forward the current year profits/losses to the retained earnings automatically.
If the company's first set of accounts covers more than 12 months, the company must attribute the profits/losses to two YAs.
-- IRAS --
If your company extended the first set of accounts for more than 12 months; example from October 2015 to December 2016 (15 months), you can create a company file with financial year from January to December and start at 2015. During first closing, two sets of reports will be printed (from January 2015 to December 2015 and from January 2016 to December 2016). Although, the first set of report covers 12 calendar months, it contains only three months of data (October 2015 to December 2015).
You should consult your accountant if you are not sure about the financial year of your company. Any change of the financial year closing, a new company file is needed.