2) If you want to make sure people notice the main idea or most important thing or message in a picture, what PRINCIPLE OF DESIGN would come in to play?

The principles of design are the rules a designer must follow to create an effective and attractive composition. The fundamental principles of design are Emphasis, Balance and Alignment, Contrast, Repetition, Proportion, Movement and White Space.

That she has to go to a later concert and tour, but there will be new songs out by billie eilish by then

Yes and no because if you know the vocabulary used you will understand it and go faster but you might not need it