Above we can see the Fact table : Fact_Sales
It contains the Foreign keys such as Date_id which is connecting to Dim_Date Dimension table , Store_id which is connecting to Dim_Store dimension table and the Product_id which is connecting with the Dim_product dimension table.
Apart from them it has one more field called Units_sold which is having the Sum of the units based on whichever Dimension we join.
So , If we want the units sold based on the Product name then by joining the Dim_Product and Fact_Sales we will get the Sales of units based on that particular Product.
By Joining Dim_Date and Fact_Sales we can get the Number of units sold in a particular time.