Once you have assigned the tags to your elements, let's create filter and dropdown widgets.
1. Open the content manager and expand the group "Tags & Filters"
2. Select which type of filter-widget you want to add
3. Enter a title and select the tags that should be included in this widget
4. You can create as much widgets as you like. You have also the possibility to adjust the filter behaviour, for example: Enable "Multiple tags selectable" to allow users to select the tag "Size S" and "Size M".