A sound card is a device you add to your motherboard if for some strange reason your motherboard doesn't have the ability to play sound already. I have literally never heard of anyone needing one since about 1995.
Maybe it's for a retro system? It's not exactly expensive.
A lot of motherboards cheap out on their audio. I had one that had a lot of EMI in the line in and swapped it out for a 30$ card like this and it cleared it up so people would stop telling me my mic sounded like shit lol.
I actually had to add a dedicated sound card to my PC because the onboard one shat itself and died somehow, and it was way cheaper than a new motherboard.