You can filter a gallery two ways: using a stream or a category.
Filtering By Stream
In the Activate -> Widget Design tab, under the Widget Styles section, click
for the widget you want to add filters to.
Confirm Enable Gallery Filter is set to Yes.
Search for and select the category you want to filter by.
Confirm Include Stream object(s) on the items is set to Yes.
Click Save.
Filtering By Category
In the Display -> Appearance tab, under the Widgets section, click
for the widget you want to add filters to.
Confirm Enable Gallery Filter is set to Yes.
Search for and select the category you want to filter by.
Confirm Include Category object(s) on the items is set to Yes.
Click Save.
