Once you have your network set up, when you create a new group you'll have the option to designate a group that's already part of your network as a parent to the new group you are creating. In this way you can build out the structure of your network by creating new groups and choosing appropriate parents.
The parent you choose controls the way data will flow within the network. When an activist takes action, the data collected on that action will move from the group sponsoring the action up to the parent group, then up to the next parent group, and all the way on up to the top of the network.
If you have settings permissions for a group, you can change the parent of a group by editing it and choosing a different parent. You can also remove the group from the network by choosing no parent. If you change the group's parent, all the data collected by the group going forward will be sent to the new parent rather than the old. Data that was previously collected will not be moved, copied, or altered.
A note on structure: You cannot create loops or orphan part of your network. For example, you cannot set as the parent a group that is a child of the group you're editing (creating a loop). You also cannot remove all parents from a group if that group has children (orphaning a section of the network).