Components are the fundamental building blocks of React applications. They allow you to think about your UI as a collection of independent, isolated pieces.
1The Component Philosophy
Functional components are simple JavaScript functions that return a React element (JSX). They are the standard for modern React development. The most important rule to remember is PascalCase: all component names must start with a capital letter. This is how React distinguishes your custom components from standard HTML tags like div or span.
2Nesting and Composition
Instead of one giant file, React encourages Composition. You build small components like Button, Input, and Card, and then combine them into larger ones like LoginForm or Dashboard. This 'LEGO block' approach makes your code highly reusable and much easier to debug because each piece has a single responsibility.
