Yeah, that link has good pics :xyxthumbs
Here's a description of how I set mine up:
There's a quick disconnect (with a black ring on it's female half) that connects the pistol grip to the "body" of the foamgun (the part with the sliding brass mixing valve). Pull back on the black plastic ring and you should be able to separate the pistol grip from the rest of the thing.
Your shutoff replaces the pistol grip. If you're careful, you can use a pair of Channel lock pliers to unscrew the female quick d from the pistol grip and you can use that on the shutoff.
I have mine set up like this: Hose end screws into the shutoff, with a female quick d screwed onto the end of it; then the male quick d that's attached to the body of the foamgun fits into this.
So the male quick d that sticks out of the foamgun plugs into the female quick d on the end of the shutoff.