How do i access state of one reducer in other in react redux. State flow between reducers and store

I'm an absolute beginner in react-redux and I watched many videos and articles,docs and couldn't understand how the state flows between reducers and between store to reducer.

I am having state for each reducer like this

const initState = {todos:[]}

cont reducer = (state=initState,action) ....

Reducer 2 similarly with different state

initState2 = {todo:""}

reducer2 = (state=initState2,action) ...

And then I import and combine the reducers. Here I am using two different reducers which have different states and is it the right way of doing things ? If so, How can redux be called single state if each reducer have its own individual state.

Don't we have a single state in the store which is accessed by all the reducers and dispatch actions to change state of store directly instead of changing the reducer's store. Any help is appreciated and it may seems like a silly question but filling the gaps is really important and many beginners have same doubt as mine and please do help. Thank you