The days of amplified soundcards directly driving speakers are long gone.
Every PC speaker set you would buy now is amplified.
In a 2 speaker set, the amplifier will be in one of the spekers (will have a mains pwer lead or adapter connected).
In 2.1 or larger sets, the amplifier is normally located in the bass unit.
2.1 is stereo satellites with a bass unit, normally driven as a 2 channel, with the speaker system seperating the bass to the bass unit.
5.1 is perhaps the most often seen, with front left & right, rear left & right, front centre and bass, each driven by seperate feeds from 3x jacks.
7.1, using the full 8 channels, adds a pair of side surround left & right.
NB. Just because it is capable of 8 channels, does not mean you have to go for an 8 way set. Setting them all up in proper positions can be awkward, so a 5.1 or 2.1 can be more satisfactory in general use.