These three blurbs live at the bottom of the Terminology & Site Copy card on Settings › General in the admin. Expand the card if it's collapsed, and click Save Settings at the bottom of the page when you're done.
If present, this appears under the Login button in the mobile app. Use it for anything that helps a member get in — for example, "Your initial password is the same as your Student ID."
If present, this appears on the first page of new user registration. It's the proactive way to explain any registration rules you have in place. Members will still get error messages when they break a rule, but saying it up front means fewer of them.
Shown in the footer beside the copyright mark. Mostly used for copyright marks or other legal text that has to be displayed.