Let's say I have:

Product
id     name
303    Milk
404    Pasta


Sales
id      product_id   amount
20       303           32,3
23       404           29,2



The dimension table will then have:

dim_product
product_key    product_id    product_name
2002           303           Milk
2003           404           Pasta


And THEN, in my FCT_SALE table, I must have:

FCT_SALE
sale_key    sale_id      product_key   amount
203          20          !!!2002!!!    32,3
204          23          !!!2003!!!    29,2