detecting circles

so i found this video:
https://www.youtube.com/watch?v=BfQxqqtZaHM

basically what i want to do, is detect circles inside an image that I have in a picturebox, but the problem i'm having is that I don't really understand the code, and I have no idea where to begin. Could someone point me in the right direction?

It looks like he is using the emgu namespace from here. I haven't perused it, but it does indeed look like some pretty cool stuff.
kevin