The Standard Collection allows you to manually manage the assets that are in it.
Assets can be dragged from anywhere in the project and drop in either the asset area or on the collection item in the tree view area.Alternatively, the item in the Project Browser context menu can be used to add a given asset to the current collection.
When a folder asset is added to a collection, all of the assets in that folder are added to the collection instead of the folder itself.
Assets can be removed using either the Delete key to remove the select assets, or using the context menu item.