How is Disk Usage Determined? When I open my internal hard drive, which is also my start-up disk, Finder lists my account (I’m only user) as taking up 123 GB.

I double-click on my Home folder and sort items by size. Adding all folders containing over 100 MB, I only get about 22 GB. That leaves about 1 GB’s worth of files.

Where are the missing 100 GB?

I ran df -h under my Home folder, which shows about 101 GiB occupied. However most of that is taken up by the Library. What is this folder and why is it so large (93 GiB)?

I also ran Daisy Disk to map my drive. In addition to the 92 GB in the Library folder, it reports that iCloud Drive is using 55 GB and that a section it denotes as 'hidden spaces' is using 80 GB. Why does the iCloud Drive use 55 GB on my disk and what could 'hidden spaces' possibly be?
The ~/Library folder is where the system stores different things(settings for apps, steam games, iOS backups, downloads of iOS apps from iTunes and etc.)

You can look at the folder by going to your home folder in Finder, press Command(⌘)+ j and check the box that says "Show Library folder"