where can i get more knowledge about "bar code"?

Answer 1

You can get more knowledge about almost anything on Wikipedia. (Usually more knowledge than you ever knew you needed!) Yes, even barcodes have an in-depth article:

http://en.wikipedia.org/wiki/Barcode

Answer 2

you mean the little thing the cashier scans so that you can pay for your stuff? what kind of knowledge do you want about that? Generally bar codes consist of 12 numbers. I've noticed that bags of fruit and veggies always start with 033383 but the rest of the code is different for each thing. or do you want to know how it is the computer reads the little bars cause that i can't help you with. Also the barcode has to be flat or it won't scan.