There isnt a chapter on "sleep mode" because its not something you can activate. the car will go to sleep on its own, without any intervention or action from you, provided you dont do anything that keeps it awake.
The car can not "sleep" and take pictures, so sentry mode keeps it awake, for example.
Its actually pretty simple. To get the car to sleep without you having to think about it at all, simply ensure sentry mode is off, dont access it via the phone app (it has to wake up to display information in the app), and dont install any third party applications such as teslafi, stats etc.
The "discussion" comes in, when people want to use those apps, and have to make sure they are configured properly.... or "check on the car" all the time in the tesla app, forgetting that sentry mode means the car is awake (thus not sleeping).