In the bitbucket app page, I see there is a client ID and a secret. So far, there is no guidance as to how this configuration items can be used and in what flow they are used. Is there any pointer to the documentation or any help as to how they can be useful?
Client ID and secret is used for authorising your app to make API calls to Bitbucket. There are various ways you can do authorisation. You can find info about it here, which explains the differences between different authorisations with sample apps.