how do you make an HR code to advertise for something?

[Caitlin]

looking to advertise something on a flyer so people can scan the code on hphone and a video can play

[Jake]

you may be talking about a QR code, just do a web search for "QR code generator" there are plenty
http://keremerkan.net/qr-code-and-2d-code-generator/
http://zxing.appspot.com/generator/
http://goqr.me/ does 1000x1000 size
http://qrcode.kaywa.com/

Some tools will have a menu of code types, you want a URL, a tip, use a url shortener service to reduce a long youtube address to something that generates a less complex QR code. With some shortener services you could alter the destination of the QR code after it's already printed.