You need a sound card on your PC - some motherboards have built in sound, others need to be added.
Much will depend on how old the PC is - some have 2 outputs, others 3 and so on.
standard stereo speakers
2.1 - 2 speakers and a subwoofer
4.1 / 5.1 / 6.1 / 7.1 - speakers and subwoofer.
If you know the motherboard you have, or if you have a sound card, you can get the details of what it supports.
They will all amplify DVDs, videos etc.