Ratio to report is an analytic function. It computes the ratio of a value to the sum of a set of values. If expr evaluates to null, then the ratio-to-report value also evaluates to null.
The set of values is determined by the query_partition_clasue. If you omit that clause, then the ratio-to-report is computed over all rows returned by the query.
select nazwa, value, round(ratio_to_report(value) over (),2) as rat from ( select 'kazik' as nazwa , 1 as value from dual union select 'magda', 2 from dual union select 'jan', 3 from dual) t1
More information about this function you find in documentation in THIS adresses.