Hi there. I had the same issue. After watching this Youtube I figured out how to do it. Within the category selector (available only on a header element), choose the layer that contains the item you want to apply the filter on. Under the Data tab, choose "Grouped Values" then choose the field that represents the category your want to filter. Now go to the Actions tab and select your filters. You can filter any layer in your app, but it has to have a "target field" that relates to the "source field" you chose in the data tab.
I hope that helps. I watched the Youtube video several times, stopping it where she was choosing filters so I could see exactly what she was doing (she works really fast).
