Furniture is a general term; it includes within it many different items. If I ask you to form an image of furniture, it won't be easy to do. Do you see a department store display room? a dining room? an office? Even if you can produce a distinct image in your mind, how likely is it that another reader will form a very similar image? Furniture is a concrete term (it refers to something we can see and feel), but its meaning is still hard to pin down, because the group is so large. Do you have positive or negative feelings toward furniture? Again, it's hard to develop much of a response, because the group represented by this general term is just too large.
We can make the group smaller with the less general term, chair. This is still pretty general (that is, it still refers to a group rather than an individual), but it's easier to picture a chair than it is to picture furniture.
Shift next to rocking chair. Now the image is getting clearer, and it's easier to form an attitude toward the thing. The images we form are likely to be fairly similar, and we're all likely to have some similar associations (comfort, relaxation, calm), so this less general or more specific term communicates more clearly than the more general or less specific terms before it.
We can become more and more specific. It can be a La-Z-Boy rocker-recliner. It can be a green velvet La-Z-Boy rocker recliner. It can be a lime green velvet La-Z-Boy rocker recliner with a cigarette burn on the left arm and a crushed jelly doughnut pressed into the back edge of the seat cushion. By the time we get to the last description, we have surely reached the individual, a single chair. Note how easy it is to visualize this chair, and how much attitude we can form about it.
The more you rely on general terms, the more your writing is likely to be vague and dull. As your language becomes more specific, though, your meanings become clearer and your writing becomes more interesting.
Does this mean you have to cram your writing with loads of detailed description? No. First, you don't always need modifiers to identify an individual: Bill Clinton and Mother Teresa are specifics; so are Bob's Camaro and the wart on Zelda's chin. Second, not everything needs to be individual: sometimes we need to know that Fred sat in a chair, but we don't care what the chair looked like.