I attempted this a while ago and I apparently accidentally deleted user threads...

I think that the default of being notified when we post on a thread means that I inadvertantly have subscribed to many notifications and I would like to turn them off.

What is the _correct_ way of turning off notifications to various threads?

If you go to the "Recent Posts" page and click on the vertical ellipsis to the far right for each topic you will be presented with the option to "Unsubscribe" from that the topic. You will have to do this one topic at a time.

Under no circumstances should you select any of the other options 

 Click your avatar in the upper right corner beside search box and select Notifications.
If it opened the menu then the notifications, in the Nnotifications page, hover the mouse below the Welcome title in the upper left part and above the Notifications title. It should show a blue border around that box with a overflow button (three vertical dots), click that and select Configurations.
In the next page that opens, you can select on or off for each of the notifications and whether to have them as email or on the site. Althouth Liferay may ignore some of your preferrences! Good luck!

 

By default when commenting on any thread, it subscribes users to that thread, because the checkbox below this editor that I am writing now, is always on, and it should be marked off each time. You moderators may have some more permissions to turn it off, although I suspect that.

If you do this make sure you scroll down to the "Message Boards" section. None of the other seventeen sections on that page will help you with your request.

Yes.