To order your categories, first navigate to the level of category you wish to sort, then press the sort button at the top of the column.

Or, to sort the items within a category, press the paper and pen icon on the desired category then click "Organise the items within this category".

In either case, the sort interface (pictured right) should then appear.

You can use this interface to move items into your priority items panel by pressing the '^' button. Once here they can be dragged into the desired order or moved back down for auto sorting.