The course homepage is the page with a description, a list of lessons, and a "Start Learning" button. Some of its behavior is controlled by the "Course Homepage" block in the learning process settings.
To customize the course homepage, open the course and go to the "Course Homepage" section in the Learning Process settings. Here you can: hide unavailable lessons, show the login button, hide the "Start Learning" button, and specify the text below it. Save by clicking "Apply."
The announcement at the top and the course completion screen are adjacent blocks of the same settings.