You will be able to edit these existing auto-responders or delete them entirely. Auto-responders need to be set up and the message which they send back needs to be created. It can be changed anytime you need to change it, or it can be deleted. The trigger is the address which is used. Messages sent to your trigger address will be responded to with a message you create.
Subject is such a standard for email.
It CAN be left blank but most email programs complain about that. What you type in here is what the receiver will most likely first see and is usually the aspect of an email which will cause them to read it now or later. The subject line doesn't have to be a single word, a phrase or short sentence can also be used. However, the subject line should be consistent with the body of the message. Keep it simple.