Here’s an explanation of how product variants work in Grosh.
A product can be milk and a product variant could be the variant of Milk sold at eg Lidl.
Grosh supports different product variants, and it is most easy to do if you use barcodes.
Scanning a barcode of an item will trigger a registration form the first time this is done for your language.
You enter the name, brand and perhaps take a picture.
This is now stored in the system for the barcode.
The next time you want to add the same product variant to the shopping list, you should be able to scan a barcode and the item gets automatically added with the information entered previously.
Note: You need to enable product variants for the shopping list in question for this to work, see more here.