A design system is everything covered in this course so far — Components, Variants, Color styles, Effect styles, a type scale — organized into one shared source of truth that every designer on a team pulls from, instead of each person rebuilding the same button slightly differently.
Any file's Components, Color styles, and Effect styles can be published as a Library from the file menu, making them available to every other file a team has access to — a designer working in a completely different file can search for and drag in the exact same Button component, guaranteed identical because it's the same source.
The Assets panel (left sidebar) is where every available Component lives — both a file's own Components ("Created in this file") and anything pulled in from published team libraries or public UI kits. Search it by name, or browse by category, and drag a result straight onto the canvas as a new Instance.
Full UI kits for major platforms — Apple's iOS/iPadOS kit, Google's Material Design kit — are freely available and get used constantly as a starting point: real, on-platform Components for every standard control (buttons, switches, tab bars, navigation patterns), so a project starts from something that already looks and feels native instead of building every basic control from a blank canvas.
A public kit (iOS, Material) is the fast starting point for prototyping and for apps that should feel native to their platform. A custom design system — built from this course's own techniques — is what a real product with its own brand identity eventually needs, since a public kit's components carry someone else's visual language, not a company's own.
What this course has been building toward
This entire reference file, built across this course, is itself a small design system — a Button component set with named variants, a documented type scale, and reusable Color/Effect styles. The mechanics don't change at any size.