If your boss asks you to do a quantitative analysis of this month's ice cream sales, he's not asking you to talk about how pleasant the customer interactions were. He wants numbers: how many cones did you sell of each flavor?
If quantitative sounds like the word quantity to you, you're on the right track. Something that's quantitative is expressed in terms of quantity. When you're trying to figure out how well your new business is doing, there are all sorts of factors you need to think about, but only some of them can be measured in numbers. Those are quantitative. The other things, like say, how pleasant the room feels, would be qualitative, a word that's often paired with quantitative.