If a steam vac has an attachment that cleans upholstery does that mean it cleans furniture like couches?

yep

Yes and more! I use the upholstery attachment for lots of things! I use it to shampoo the seats and carpet in the car, to suck up water when defrosting a freezer and to clean areas that I can't get the big shampoo machine into like corners. You can also use it on steps if you have carpeted steps, to clean mattresses and to even suck the last bit of water out of the top tank of a toilet when making plumbing repairs! Sure beats having that last inch of water running all over the bathroom floor!

And if I have a spot that requires pretreating and a little scrubbing, I often use the upholstery attachment for that, then rinse it using the whole machine.

Hi Hold the upholstery tool about 6 to 8 inches away from the sofa and spray the solution onto he sofa. Let it sit for about 3 or 4 minutes then vacuum it off the sofa ( this will allow the cleaner to work). Carpet cleaner for 14 years

sure but its not like the best way some folkes use a dry shampoo that foams then vacuums up

yes