How do the filter categories on the order plan work? e.g.: fastest moving, most urgent orders, most stagnant etc

Fastest Moving: This basically sorts by the average daily orders. Items with larger avg daily sales will appear at the top.

Most urgent orders: This sorts by the (Lead Time - Days until Stock out) X Order Quantity. The idea here is that ones with the largest difference between how many days stock you have left & the lead time show near the top, as well as items with the largest suggested order quantity. 

Most Valuable: This sorts by the Sku Cost X Stock On Hand. Items with the largest inventory value show at the top.

Most Stagnant: This sorts by the days until stock out X the Stock on hand : Avg daily orders ratio. This means that items that have a large number of days until stock out, as well as a large amount of stock on hand and a low average daily sale rate, are shown at the top.

Excess stock: This lists all items that have excess (i.e: the stock on hand + on-order amount is above the reorder point).

Stock out Risk: This lists all items that have a suggested order quantity (i.e: the stock on hand + on-order amount is below the reorder point).

Never sold: This simply lists all items that have no sales history recorded against them.