How can I find out what's taking up space on my hard drive?

Episode 1290 (1:45:58)

Aiden from Johanesberg, So Africa
Disk Inventory X

Aiden's SSD drive keeps filling up with stuff and he isn't sure what's using up space. Leo says on the Mac, he should check out Disk Inventory X. It gives him a color based representation of what's using up space and sorting by size. It even gives him the ability to move things to the trash from within the app.

There's a similar program on Windows called WinDirStat.