The ThemeSwitch is a stateless component which provides the UI to change the theme inside your application. If you want to use it, you have to pair it with a theme provider — which commonly wraps the whole application — and pass the theme to ThemeSwitch from the context provider through the currentTheme property.
The onChange property allows you to change the theme on value change. This component is made for basic usage with only light/dark/system themes. If you want to add more themes, you have to build your own component.