Barcode database sites and smart-phone barcode apps search the internet for information about the particular barcode number that has been entered or scanned. The information that is returned is generally the company name and/or contact details, relevant product information, or even where you are able to purchase a product from.
Please note that some smart-phone barcode apps only search in online stores such as Amazon.com (they don’t search in the online barcode databases). This means that their database of barcode numbers / product details is very limited. The best smartphone barcode app’s (e.g. the Zebra Scanner) search in Amazon and other online stores as well as the main online barcode/product databases.