You can open Windows Explorer and right click on folders one at a time to see how much storage they are using.
This can be time consuming and you may want to use a program like Tree Size instead.
A free reduced feature version is available for download from Jam Software at the following link: Free Treesize Software
The .zip version doesn't need installed. Just unzip the folder and run
The program is intuitive and allows you to specific which drive or folder to scan.
It will help you to identify quickly where you storage is being used.