Info. about reducers (#20642)

guide/english/redux/reducers/index.md

@@ -5,6 +5,10 @@ title: Reducers
 
 Reducers are the pure functions that take an action and an previous state and return new state. Given the same input, the reducer should always return the same output.<sup>1</sup> 
 
+In a simple sense, reducers are gatekeepers of the redux central store.
+- Components subscribe to the central data store which gets passed via props
+- In order to make changes to the data store, components dispatch actions (along with optional payload)
+- These actions gets passed onto reducers which then update the redux data store
 ### Sources 
 
 1. http://redux.js.org/docs/basics/Reducers.html