By default, your Organization will be set with a 15% Gross To Net Discount. This may not be the correct discount percentage for every company. Say, for example, you are in Australia. The typical discount is 10%. Or if you deal with varying discounts, maybe it's most appropriate to set your default to 0% and change it based on the Advertiser, Campaign, or even line item.
To change the default:
Click on your Organization Name
Click on the Settings tab
Adjust the Gross to Net Discount as desired
Press Save Changes button
When changed here, new Advertisers created will use this default value. You can change the default for the Advertiser in the Settings.