I have installed FDM into Chrome. When I want to resume a download, does FDM automatically start when you start Chrome or do I have to open it in extensions? Many thanks in advance.

The Chrome extension, like all the browser extensions, is linked to the FDM app installed on Windows.

My experience has been that, if FDM is not running, and I use a browser to download a file, it will automatically run FDM when it is not running.