When any updates for C3 is rolled out? How do we know about it, and how does it update automatically? Do we need to clear cache?
No, we've thought of it all. https://editor.construct.net will always load the most recent version, no cache clearing required.
Releases pages auto updated when new release is out as well:
https://www.construct.net/make-games/releases
Develop games in your browser. Powerful, performant & highly capable.
Does the editor informs the user that is has been updated?
Yep