On our website, we are implementing the accept cookies policy. After the user accept/decline the cookies policy what have to do? where we have to store the data, what are the data have to store. we need to use the database or have to store it on local storage
This is something that you as a developer need to decide. What do you need to do depends on what your app needs to do.
To store the "accept" you would almost certainly have to use local storage - think about what and how would you save it into a database - there is no practical way of identifying individual anonymous users other than using local storage.