Homer Simpson wanted to beat his son in video games. So he went to a video games house and asked a boy to teach him. The boy bargained that Homer had to bark like a dog. In order to beat his son, Homer did so.
And then the boy said to Homer, "you got yourself a deal, Fido".
Thanks in advance!
I'm not sure I understand the joke, but "Fido" (an abbreviation of the Latin for 'faithful' - not that all users know or care) is a typical dog's name.