Ask HN - Allowing other sites to embed Your content (eg. Hellobar, Qualaroo)

I've been searching through the source files forever and can't figure how sites like hellobar.com and qualaroo.com allow someone to embed the companies content on the webmasters site(Never was too great with javascript.) Can anyone explain, or point me in the direction of a good tutorial to walk me through this? Eventually I'd like to figure out how to personalize this based on uID (etc.), but I'll start with the basics for now. Thank you in advance for any help!