subscriptions table and settled ach payments

I see at the bottom of the API documentation page that seemingly webhooks can be created by modifying the subscriptions table. Please tell me, where do I find the subscriptions table and what do I change.

Also, I see reference to create events. Can subscriptions be created for update and delete events too.

Lastly, I’d like the know when ACH payments are fully settled and deposited. Can this be done with a subscription to payment update events and watched for the status variable changing to a specific value? Or how?