So I guess to answer the original questions what does it mean.
Making Love (Out of Nothing at all) means:
I think the "Making Love" part is referring to the emotional aspect of Love and not the physical. And in this context the "Out of Nothing at all" part means that the people involved had nothing in common, were not attracted to each other, were not compatible but still they ended up in love.
I keep on having to put "I think" and "I guess" because it is all very subjective. This is my opinion and many others may disagree with it. I may be entirely wrong.