Once you've turned this on, select a driver from the left pane of the main dispatch window. This will show all of that driver's active orders in the center part of the window. Now, right-click anywhere in that window and you'll see two options at the bottom: Optimize Pickup Addresses and Optimize Delivery Addresses. Pick the appropriate option, enter in a starting address and an ending address, and click Optimize. Digital Waybill will show you a map of the suggested Google Maps route, and you can accept or decline their suggestion. If you accept, the driver's orders will be rearranged and display in the new order in his 2-Way.
Note: the cross-order routing works either with pickup addresses or delivery addresses, and will only consider those addresses when it creates the route.