The flight contains the detailed instructions, such as targeting options, and creative that a campaign should deliver. A campaign must contain at least one flight but it may contain many depending on the Advertiser's instructions. Flights can only serve within the date ranges applied at the Campaign. (As with the campaign screens only some of the sections are required).
The easiest way to add a flight is to navigate to the campaign details page. On the top navigation bar select Traffic and then from the All Campaigns screen click on the Campaign Name you wish to add this flight to.
At the bottom of the campaign details page you will see the Flights section. Click on Add New Flight. You are taken to the flight entry page with the Campaign Name and Advertiser clearly shown at the top of the screen.
For a complete description of how to add a flight to a campain, refer to Usage Note 53894: Creating Flights in a Campaign or the User's Guide.