If you tried to scan a bar code on a packaged food item and the search yielded no results it might be that our database doesn't (yet) have that item.
If you tried to scan an item and it wasn't found, you can use the "Create New Food" function to create that item associated with that bar code. That means all future scans will show up as that item you just created.
Also, make sure the bar code is in good quality and readable. So it might help to smooth it out to remove any creases or arrange good light conditions during scanning.