Consumer prices are the prices paid by individuals when they buy goods and services. If you purchase an item for Rp100, then the nominal is the consumer price.
The statistical bureau collects the price of a basket of goods and services purchased by consumers to construct the consumer price index. Each product and service has different weights in the basket, depending on their relative importance in consumer spending.
Changes in the index over time represent the inflation rate. When inflation is high, say 10%, it means that in general, prices for consumer goods increase. High inflation reduces the purchasing power of money because, with the same nominal money, consumers could only buy less than before for the same goods with the same quantity.