Most of the guitars you see around are steel-string guitars, which means pretty much what it sounds like. Six strings, two bare steel, the other four steel wrapped in nickel or some such thing (that's the basic item; there are a hundred variations). If you hear somebody playing classical or flamenco music on guitar, it's almost certainly a classical guitar; you might also hear this referred to as a "nylon" guitar because its strings are nylon (which is an attempt, I think, to recapture some of the qualities of the historical catgut strings). Three bare nylon, three nylon wrapped in nickel or whatever. Same notes as the steel-string, played the same way, more or less. Not so different in any glaring way.
Here are some of the differences, physical and cultural. The physical ones trace largely to the fact that nylon vibrates over a wider period than steel. Because of this, the strings on classical guitars are set further apart than on steel (two inches, rather than an inch and three quarters, at the nut, the bar that marks the meeting of head and neck) and the action, or distance between strings and fretboard, is higher. This makes classical a pain for folks with small hands and a blessing for the thick-fingered. Also, of course, nylon strings are softer, and thicker, which makes them easier on the fretting fingers, and they flex more easily, which makes pitch bends easier. Plectrums or flatpicks are used almost exclusively on steel-string guitars--not because they don't work on nylon, but because nylon has traditionally been associated with the intricate right-hand work of classical and flamenco guitar, which doesn't actually work nearly so well on steel, though it can be done.
(Here's where I geek out for the benefit of a very small audience.) I have for years noticed a surprisingly deep-running analogy between the classical-steel and Mac-Windows rivalries. In each case, the vast majority of the populace is unshakably given over to one implement; in each case the basic task at hand is the same, and both options will get the job done. And in each case, I personally happen to have begun with the minority implement by simple historical happenstance.
Granted that (which is doubtless a prejudice in some degree) I tend to believe that the minority choice--the one favored by devoted artists--is a subtly more powerful one. Bends, which are commonly associated with blues, are a great deal easier on classical guitars, which are not typically used by blues players--a dramatic difference. Vibrato is virtually unknown to steel string guitars below the seventh fret, and in my opinion (on a more subjective question) the classical guitar has a far greater range of expression, where steel, barring any electronic tinkering, pretty much goes from bright to bright. I am far less qualified to speak about OS differences, honestly, but I do think Macs have a more straightforward interface than Windows, fewer assumptions made for me by the machine--and I believe their raw processing power has been in the lead for a while, though that goes back and forth, of course. Of course, the Windows style of minimizing is better (and has been co-opted for that reason in OSX) and steel strings get better harmonics. It isn't an entirely unilateral difference. But still it isn't any photo finish.
Oh, and in each case it's worth noting that the majority instrument is historically a knockoff of the older and better one--but the general public is totally unaware that any rivalry exists, having been hypnotized by an inferior product.