Full Price Sales are those that do not include a Promotional Sales, while Total Sales include ALL Sales.
Orders are the amount of orders you have for the day and you can have multiple units sold in one order. Units is another name for products and the number is the amount of products / units you sold for the day.
Cancelled Orders are automatically deducted appropriately from the Dashboards once the Customer cancels the Order. While Refunded Orders are not deducted from the Dashboard totals, the number of Refunds will be displayed on the bottom right of each box as shown below.