In a Short: you have to use
Aggregate Functions (Transact-SQL)[
^]
I'm bit lazy today (as it's a sunday) and i don't want to analyze your database diagram, so... general tip:
To get the quantity of products:
SELECT Product, COUNT(*) AS Quantity
FROM SaleTable
GROUP BY Product
To get the value of sale:
SELECT Product, SUM(Price) AS TotalSale
FROM SaleTable
GROUP BY Product