The Commercial papers are "Unsecured" Promissory Notes. Since these papers are Unsecured and don't have any collateral security, only highest credit rated firms are able to sell their CPs at reasonable price and "Trust" over the company matters a lot in CP Business. The maturity of the CP is from 7 days to 1 year.
Usually the CP is sold at a discount value and redeemed at face value. For example, if Suresh buys a CP with face value at ` 100 at the discount value of ` 98, when he redeems the CP on its maturity which may be anything between 7 days to 1 year , ` 2 would be his earning.