Closed padlock:
When there is a closed padlock next to a page, it means that to edit it you need to be logged in to the front end. This is because these pages are only accessible by registered users. To do this, you can go to Users and pretend to be logged in with your front-end user (not administrator). This happens on pages such as registration, my courses, home with login, for example.

We recommend always creating your own front-end user, so that you can simulate session when you think it is necessary and test.
Open padlock:

When there is an open padlock next to a page, it means that to edit it you must log out of the front end. These pages are accessible without the need to be logged in. This happens in the public front, login or registration page, for example.