Jenna, this would be the video you watched from the Help Center, correct? Please do try that on your end as well; it would be easier to explain with the example shown in the video.
Tag few entities with new terms based on the 'Application' ModelTag. Go to your Mashup, click on the green plus (add entity) and choose the 'Applications' ModelTag. Now, select the GetVocabularyTermUsage service and bind All Data to the Pie Chart. Add a Grid widget as well, and bind All Data to it. Select your Pie Chart and in the settings pane on your bottom left, select 'name' for LabelField and 'value' for ValueField. If you view your Mashup, the name/ value displayed on the Grid would correspond to your Pie Chart's display.