Each device can have labels associated with it, which are key value pairs. These labels can be used to group devices to control the deployment of your application. Scheduling rules are used to determine if an application should be deployed by comparing what labels are on or not on a device.
Click on the + to add a new label. After entering the key and value, make sure you click on the save icon to save the label. If the key and value are still displaying textboxes, then they have not been saved.
Once a label is created, you can only edit the value of the label. If you want to update the key, you will need to remove the label and re-add it to the device.