To get better understanding of aspect ratios in general, explore your TV and computer monitor settings, not to forget the camera. They all have aspect ratios!
Open Adobe Photoshop software on your computer.
Q.1 What frame size will you use for 4:3 aspect ratio?
Q.2 What frame size will you use for 16:9 aspect ratio?
Q.3 If you want to make a movie, showing view of the mountains, ocean, desert, jungle etc. Which aspect ratio will enhance the cinematic experience?