Oh my goodness *g - let me think, if my english is so good to explain.
When you wrote a mod and your product (product.xml) lets you know the productid.
example: product=
myproduct.
Next is, you post your mod into your forum. At the mod-settings you enter
myproduct as productid.
Also in the product (product.xml) the versioncheck url is:
http://....../modsystem_versioncheck.php?product=myproduct
Hope this will help to understand