Please see below for step-by-step instructions, followed by a video tutorial.
An Agency represents one or many Advertisers and are used for insertion order submission and billing after a Campaign has run. To create an Agency, begin by going to the "Agencies" in the left toolbar.
1) Click "Create Agency" button
2) Enter Agency Details
The only required field for the Agency is "Agency Name".
In addition to Agency Name you can also specify:
an External ID for the Agency
For each Agency Contact you can include:
Contact Type (Agency, Media, or Billing)
There's also a section for Billing Information for the Agency. You can specify:
Advertisers who are not working through an Agency
If an Advertiser is buying direct and is not represented by an Agency, they should still be added as their own Agency.