This repository is where you define your AWS Organizations structure in the form of folders. In the folders you can define AWS CloudFormation Templates and Service Control Policies (SCPs) that correlate to those specific Organizational Units (OU).
You can define global.yml or regional.yml templates that will be applied to either the main region (as defined in adfconfig.yml) in all accounts for a specific OU and if regional is specified, all regions within accounts in that OU. To create Service Control Policies, create a scp.json file in the Organizational Unit of your choice, for more information please see the admin guide for ADF.