A range allows you to specify a date, albeit imprecisely (for example, "John Smith died some time between 1941 and 1943"). Do not confuse this with specifying a period (see the Period tab).
If you know the year, but not the month or day (or the year and month but not the day), you do not have to use a range. It is easier and better to use the Date tab, and omit the missing details.
See Simple Date Fields for help on the date fields.
With fact dates (dates of events or attributes, displayed in the Facts tab of the Property Box), you can optionally also enter a separate sort date.