I ant to make simple surround sound system including a subwoofer and 4 speakers from pc audio as input.
What should I do.

 

I ant to make simple surround sound system including a subwoofer and 4 speakers from pc audio as input.
What should I do.

I'm going to assume you mean that you want to assemble a system, not actually build one from scratch. That would be difficult and perhaps impossible. You didn't mention video. To reproduce audio, you don't need a 5.1 system. Two good speakers is fine, or two smaller ones with a subwoofer.

Buy yourself a good AVR (audio-video receiver). Systems capable of 5.1 audio have been around a long time now and many are available on the used market, if you want to save money. Whatever you spend on the receiver, plan to spend more on the speakers. These are the weakest links in most systems because buyers tend to focus on the AVR specs. Speakers are much harder to compare and buy, but they make the biggest difference in your system.

It's essential that your system is able to decode the source material and maintain the highest possible quality from the source all the way to the speakers. There are many options to accomplish this. Decoding can happen at the source (your PC, presumably) or in the receiver. Using the receiver is usually the preferred approach. The technologies you need to have on your AVR depend on your source material; whether it's blu-ray or DVD quality, the codecs used to package the sound (Dolby True-HD or DTS-MA and so on), the interface you intend to use (HDMI, bitstream, etc.) and so on.

 

To get surround sound from your PC it must have a digital audio or HDMI output.
Do you have either of those?