install
        import and use 

        slice 
            import 

            define
                name 
                    initalsate, 
                    reducer(s)
            export, 
            
            import slice in store.js

        use slice 
            dispatch 
            useSelector
        
        redux toolkit query 
            import 

            define 
                name 
                basequery
                endpoints
            
            export 

            import in store.js 
                middleware

            use 
                import 
                use

redux 
    install 
    import and use      // store.js 

    reducers            // reducers 
        combineReducers     > parent reducer    > index.js 
            reducer         > tiny reducer      > location.js 

    action creator      // helper function      > generate action type and payload for reducers

    provider            // connect redux with react     > provide state to react 

    use 
        useSelector 
        useDispatch