Reducer is a function and it takes two arguments
(action, currentState) -Process-> Returns new state
Action creators creates an object, sends it to reducer, out comes a new state
Takes a bunch of functions and returns a new function
const lotsOfFuncs = compose(makeLouder, embolden, Yolo)
It's a way of chaining functions
React only has concept of one reducer. We can split up reducers then use combineReducers to combine them into one file.