there should be a flange at the end of that chain, if there isnt then your f$%^d, if its still there then:

lower the chain until the flange is resting on the top of the tire. stick the flange into the center whole of the rim, you may have to prop the tire up 20 to 30 degrees on one side to make the chain and flange reach thru the whole. then start cranking till the spare is snug.