How is my storage being used on my MacBook Pro?

According to: How to free up storage space on your Mac - Apple Support

"To begin, choose About This Mac from the Apple menu , then click Storage. You'll see an overview of your free space and the space used by different categories of files, including apps, documents, and photos:"

Another option is to use: WhatSize

Then click on manage storage after doing the above and it will tell you exactly how much is where.