An efficient product offers its users a consistent experience into the various entry points they have with the brand (mobile and web apps, emails, landing pages, social networks...)
Therefore, a design system is a strong asset to effectively communicate with its audience and help the teams creating content. Because it defines various rules and usages, it also give them more freedom into these boundaries.
For instance, let's take two engineering teams working on the same project. They're more likely to create a unified user journey if they agree on using common constants, components, page architecture principles. Otherwise, they would need numerous meetings and product reviews.
What can we found in a design system ?
- A graphic charter where (colors, spacings, shadows...)
- a UI kit that designers use to create mockups
- one or many component librairies depending on the target plateforms and development frameworks (iOS, Android, React...)
- A development and architecture documentation to be able to use the component properly
- A contribution guide, because a design system is a living thing and should be able to accept contributions from users on the field
A design system is a service which the users are the content creator in your company, and not a bunch of static assets (Figma components, React component...), that's why it is recommended to dedicate a team in charge of maintaining it. As it is at the crossroads of several jobs, you should pay attention to have a multidisciplinary team : developer, UI/UX designer, product owner, content manager...
Some companies published their UI kits and component libraries. They can help you to figure out how it would look like by the end.
Don't forget that those links are only showing the tip of the iceberg: as said above, a design system is a living product and the websites are not showing the teams in charge, the contribution process, the interactions between people, the research and testing phases...
If you want to dig deeper into design system creation and support, I recommend you this interview of Clément Menant, UX design in charge of Airbus design system, who used to work at Troopers before I joined the team.
Disclaimer: the podcast is in French, but if you know some good English ones, I'll be happy don't hesitate to share them so I can link them too.