We have a separate sink sprayer that's off to the side of the faucet. Something in the sprayer assembly broke and the water now comes only out of the sprayer and not the main faucet. I called Moen, and they sent me what they thought was the same sprayer, but it's different. I thought I could just undo the top part of the new sprayer and twist it onto the bottom of the old one, but one's an innie, and ones an outie ;-). They sent the full assembly with a new hose.

Looking under the sink, I see where the hose attaches. There is place where it threads in, and a small valve or knob right under where it attaches. It's a metal oval about 1.25" long and it attaches to a plastic shank. It doesn't look like the other blue, lacy type round knobs with open areas in a design. Is this a knob to secure the hose, or is it a water valve? Does the water need to be turned off to change out the hose?

Would really appreciate some help, as I don't want to flood my kitchen. Is this doable by someone who doesn't know anything about what goes on under a sink? Thanks ;-).