1. Single source of truth: The global state is stored in a single store
2. State is read-only: State can only be changed by dispatching actions
3. Changes are made with pure functions: Reducers are pure functions that specify how state changes in response to actions

The Redux store is a single JavaScript object that holds the complete state tree of your application. It provides methods to:

• getState(): Returns current state
• dispatch(action): Dispatches an action to trigger state change
• subscribe(listener): Registers a listener function

import { createStore } from 'redux';
const store = createStore(reducer);

Actions are plain JavaScript objects that describe what happened in the application. They must have a type property and can contain additional data (payload).

// Action object
const addTodo = {
  type: 'ADD_TODO',
  payload: {
    id: 1,
    text: 'Learn Redux'
  }
};

// Action creator function
const addTodoAction = (text) => ({
  type: 'ADD_TODO',
  payload: { id: Date.now(), text }
});

Reducers are pure functions that take the current state and an action, and return a new state. They specify how the application's state changes in response to actions.

const todosReducer = (state = [], action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return [...state, action.payload];
    case 'REMOVE_TODO':
      return state.filter(todo => todo.id !== action.payload.id);
    default:
      return state;
  }
};

• Actions: Plain JavaScript objects with a type property
• Action creators: Functions that return action objects

// Action
const action = { type: 'INCREMENT', payload: 1 };

// Action creator
const increment = (value) => ({
  type: 'INCREMENT',
  payload: value
});

Using React-Redux library:

1. Wrap app with Provider component
2. Use useSelector hook to read state
3. Use useDispatch hook to dispatch actions

// App.js
import { Provider } from 'react-redux';
<Provider store={store}>
  <App />
</Provider>

// Component
import { useSelector, useDispatch } from 'react-redux';
const todos = useSelector(state => state.todos);
const dispatch = useDispatch();

The Provider component makes the Redux store available to all nested components. It uses React's context API to pass the store down the component tree without manual prop passing.