Looks like you need a new "branch wye" (that's the name of the piece of pipe with the little arm on it that the hose is connected to). It connects to the "basket strainer" (the piece that goes through the sink opening) using a "slip joint" nut and washer. You should be able to take it off with a pair of adjustable pliers. Make sure you have a new "flange washer" for the connection between the "branch wye" and "basket strainer". If you take this photo to a hardware store or plumbing supplier, they should be able to outfit you with the proper parts.