connect amp to computer with an adaptor.
usually the adaptor is a cord with the correct connector on each end.
you need to know what the impedance of the speakers are to get the right amp.
100 watts RMS at 4 ohms is only 50 watts RMS at 8 ohms.
maybe you buy a 100 watt amp and only give the speaker 50 watts.
a digital multimeter should get you started with the impedance when you connect the multimeter to the speaker tabs.
maybe you get an old receiver off ebay that is only 2 channels.
they still sell some newer 2 channel 'receivers' at the stores.
but they are really only an amplifier with a radio tuner.
the amplifier will connect to the soundcard, as you would expect from your knowledge gathered that brought you this far.
the speakers connect to the amp.
what SPECIFIC question do you want to know?
there are articles and guides all over the internet about connecting an amplifier or a receiver to the computer.
it is about as simple as computing 2 + 2 = 4
plug them into the computer with an amplifier and they will become speakers for your computer ..?
i dont see where you are having any trouble.
if you are looking for amplifier classes and their differences, start here:
http/en.wikipedia.org/wiki/Electronic_amplifier#Power_amplifier_classes