Use Insert Columns to add new empty columns to your document. The command is
only available if you have already defined a staff.
Steps
Choose Columns from the Insert menu.
Type the number of columns you want to add to your staff.
Choose the Before button to insert the new columns before
the current column or
Choose the After button to insert the new columns after the current column.
If you want to save the number of columns added for the
next time you insert columns, choose Use as Default.