Just get a basic amp or receiver, either new or find something used on craigslist or FB Marketplace, or even your local Goodwill. If you need something basic that doesn't take up a lot of space, here is one:https://www.amazon.com/Audio-Amplifier-Receiver-Integrated-Speakers/dp/B076P2VS9H
You'll also need a cable to send audio signal from your computer to your amp/receiver. Cable type will depend on the type of audio connections that your computer has.
If you have very critical ears and want to ensure best possible quality, you might also want to invest in an external DAC as most DACs built into computers are not of high quality. Really depends on what you'll be listening to and how OCD you are about audio quality.