A range allows you to specify a date, albeit imprecisely (for example, "John Smith died sometime 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 to use the Date tab, and omit the missing details.
See Simple Date Fields for help on the date fields.