This mini tutorial will cover how we use barcode scanners. This isn't necessarily an Arduino project, but it is a tool that we use every day when shipping packages - instead of entering in invoice numbers, we use a barcode scanner. That way we don't have to worry about humans making typos!
This kind of scanner connects via USB to a computer and has a laser/sensor with a rotating mirror, the laser constantly scans in front of the opening, so its very easy. There are also less expensive wand types where you have to 'stroke' across the barcode (such as the old cuecat) and more expensive 2D rotating ones such as those at checkout counters where you can have the barcode rotated and it doesnt matter.