Yes, a subwoofer only makes that Brrrm sound, and only does so on audio tracks that instruct it to do so, in a manner of speaking.
The subwoofer's position does not matter at all because of how sound at that low frequency travels (or propagates, to use the technical term).
Placing it on the floor near the other speakers should be just fine. A soft surface that minimizes vibration buzzing is probably best.
More information, not exactly necessary to read unless you want to know more and are interested:
Difference sizes, masses, and contruction types of speakers produce different sorts of sounds differently. It is difficult to build a single element speaker that will faithfully represent a full range of audible and sub-audible (felt, rather than heard) sounds. For this reason, many of the better speaker systems use multiple speaker elements to produce the wide range of sound more faithfully.
Small and light but very stiff speaker elements are better for very high frequencies (high sounds) but will not produce a real bass sound. As you go lower and lower in frequency you want generally larger and more massize speaker elements for each "section" of sound.
For instance, a set of 4-way speakers I picked up at a garage sale many years ago had four speaker elements (the "4" ways). A small 2-inch tweeter than was shielded gave off a very nice clear high range. Two larger cones at 4 and 6 inches served to produce a nice mellow mid-range, and a huge 14" cone with a magnet that must've weighed nearly 2lbs produced a rich bass that wasn't necessarily very thumpy or boomy.
Because it's hard to fit a 14" cone near the average desk, subwoofers are generally make with 3 or 4 inch cones of very thick paper with massive magnets that will produce a very sharp, booming bass note, which is excellent for games and most movies. It won't make a very smooth bass if you're, say, trying to play a beautiful concerto or other symphonic piece. The drums will sound OK but the double-bass will simply not sound like it's supposed to. Even for all it's trade-offs, though, a good subwoofer will still work much better than a simple stereo speaker setup because it offers that speaker that is precisely tuned for giving a good thump. The normal small desktop speakers just can't do it.
The human ear is relatively good at picking up the direction of most higher frequency sounds because these sounds tend to bounce around the environment in specific and predictable ways. For this reason you generally want your high- and mid-range speakers to point at where you'll be sitting, and even better, they should be pointing at your ears.
Low-frequency sounds don't bounce off things so much as they go through things, and because the wavelengths they represent are significantly larger than your ears (and even than your head) you have a much harder time telling where they are coming from. This is a major benefit of helicopters in military operations. The whump-whump-whump of their blades, while loud, is very hard to pinpoint directionally and so people cannot tell where they are coming from. For this reason, the subwoofer can, and should, be placed on the floor with the only requirement being that a soft floor is better than a hard floor to prevent vibration buzzing.
