Advanced products in Magento are a way to consolidate product variants onto a single product info page in the front-end. The variants themselves have their own SKUs and stock management. This is very powerful – it allows you to let customers search for the individual variants, but browse only to the consolidated product pages. (If that’s the implementation you want – you could also let customers browse the individual SKUs.)
Configurable Products let your customers select the variant they desire by choosing options. For example, you sell t-shirts in two colors and three sizes. You’d create the six variants as invidivual products (with their own skus) and then add these six to a configurable product from where customers can choose size and color, then add to cart. If desired you could also have customers search for “red medium t-shirt” and land on the specific page for this variant.