React Redux

• redux provides an empty store where application state can be manufactured.
• You tell the store what to create as the application state, how to update the application state (thru reducer)
• store = Redux.createStore(reducer)
• Reading from the application state in application is straight forward: 
• store.getState()
• Updating the application state is by triggering the update logic in the store by dispatching the actions.
• store.dispatch({type: 'increase', graceMarks: 5})
• NOTE: When you update a state, you don’t update the state but rather create a new state out of old state.
• You can even subscribe to store to get the status on the updates.
• state.subscribe(state.getState())

• react-redux provides couple of additional facilities, Provider and connect.
• Provider to provide the store to the root component.
• Connect passes state, dispatch actions to child component. 

A sample using just redux:

// importing createStore from redux

import {createStore} from 'redux';

// Creating a reducer

const sampleReducer = function(state, action){

    if (!state){

         state = 0;

    }

    if (action.type === "INC"){

         state =  state + 1;

    }

    return state;

}

// Create a store. Passing in the reducer that i created above

const store = createStore(sampleReducer);

// subscribing to store to see the updates

store.subscribe(() => {

    console.log("state changed ", store.getState());

})

// start dispatching actions to store.

store.dispatch({type:"INC",payload:"something"})

Easy to learn: https://www.kirupa.com/react/introduction_to_redux.htm

There you go… You create a reducer, you create a store and then whenever you dispatch actions, the reducer or multiple reducers will act upon on that store.