As the processing for media and materials is similar we will only describe the way for the materials.
Step by step guide
If you want to classify materials in the Global Assets, go to Material and select your selection of materials.
Now you can go to Actions and choose Classify.
Now a window with the filters opens. Define your structure classes in the filter and click on Selection.
Now you can set the filter in your material manager so that only the selected materials are displayed.