If you're an education customer, to add Device Seats you need to place an order with your reseller. Adobe then creates a Deployment Pool for the products ordered. For example, if you purchase 100 Creative Cloud All Apps seats and 50 Photoshop Single App seats, two deployment pools are created. After deployment pools have been created, Creative Cloud Packager shows you Device License option under the License Type options. On selecting this option, you can view and select a deployment pool to use for the package. After installation, the package will attempt to activate. If activation is not possible at deployment time either due to no Internet connectivity or proxy configuration, then the package continues to run and attempt silent activation for seven days before it ceases to function.
If you want to know how many machines your package has been deployed to, you can open up Creative Cloud Packager and check the Deployed To field.
For more information, see Create packages with device licenses.