I will give you some examples, related to the options mentioned:
First example: We have an ID as abcdefg if we select the option “Show first 4 characters” the value will be returned as abcd***. Otherwise when we select the option “Show last 4 characters” the value will be returned as (three asterisks + defg) . So, one option returns the first 4 characters and the other the last 4. The other characters are mask with asterisks.
Second example: we have a date value as 2014-10-20 03:04:09 when we select the option “Only year” the value will be returned as 2014-01-01-00:00:00. So, it only shows the real year and the other values are reset.
Last example: when we select “redact” it returns a predefined masking value depending on the field type. For example if we have an ID of type text abcdef it will return the value masked with asterisks. If we have a date as 2014-10-20 03:04:09 it will return the real year and the other values are reset as 2014-01-01-00:00:00. If we have a number it will be returned as a 0 value. Finally, with other types of values annual value is returned.
Hope this helps!