MFP iPhone App Nutrition Scanning

Options
Can someone tell me how to use the App on my new (well, as my sister says, "brand used:)" --gift from my daughter when she got her 5-- iPhone 4 to scan barcodes (is it, or those square ones?) to enter Nutritional Info right into my diary? I read at the app d/l that it could be done, but have not figured it out yet. Thanks! Gyps