The "Union" mode will give all the results that match any of the selected filter values. If an item matches at least one of the selected filter values, it belongs in the "Union". Think of this as a big "OR" statement.
The "Intersection" mode will give all the results that match all of the selected filter values. If an item matches every selected filter value, it belongs in the "Intersection". Think of this as a big "AND" statement.
The "Exclusion Union" mode will give all the results that do not match any of the selected filter values. If an item matches any of the selected filter values, it does not belong in the "Exclusion Union". Think of this as everything outside of the "Union" of the selected filter values.
The "Exclusion Intersection" mode will give all the results that do not match all of the selected filter values. If an item matches all of the selected filter values, it does not belong in the "Exclusion Intersection". Think of this as everything outside of the "Intersection" of the selected filter values.