Different people may create different out of office messages based on what information they want to convey. It can be a simple notification of your absence and the date of your return. Your message can also point the person to some other person or resources to help them when you are away. Let us look at some of the most common examples and templates you can take help from when creating your auto-response out-of-office message.
Mine tend towards the latter for both internal and external and only get a little more expository if it’s a closedown period and I’m adding leave to one end of it, but that’s a simple “The organisation is shut between X and Y. For emergencies during this time please contact Team. I am on leave between Z and B and will not be accessing my email during this time. Please contact Email Address if your enquiry is urgent otherwise I will attend to your email as soon as is practicable upon my return.”

I’d side-eye if an OOO for a couple of days off said that, unless someone was in an unusually time-sensitive role. But if someone’s out for long enough that there’s an alternate contact provided, that’s long enough for them not to be wading through missed emails when they get back.
Protocol for when you should use an out-of-office message will vary by job and industry, but generally, you should set an OOO message when you’ll be out for two or more days.