From the dashboard tap on the paper and pen Icon in the middle of the screen.
From the customer list, select the customer you would like to invoice/order.
From your Product list tap on the filter option on the top right as shown below.
Select the filter SORT BY SALES and change to SORT BY MOST SOLD TO CUSTOMER and tap on DONE at the top right.
You should now only see the products that are sold to that customer.