Write a JavaScript function whose name starts with a capital letter, and have it return JSX. You can then use that function name as a custom tag inside other components.

Because React uses capitalization to distinguish custom components from built-in HTML tags. A lowercase name is treated as a DOM tag like div, while a capitalized name is treated as a component.

Props let you pass data into a component so it can render differently based on that data. A greeting component that takes a name prop can greet anyone, instead of being hardcoded to one name.