iCloud drive taking 58 GB on my internal SSD. Why is that? I have read online, from multiple sources, that icloud drive is like Google drive or Dropbox, so why would iCloud drive take up 58 GB on my internal drive. I thought putting files in the iCloud drive was storing them in the cloud.  Google drive and Dropbox doesn't take up a lot of space on my internal drive. Why is iCloud Drive using so much space on my internal drive?
Depending on settings, for both Dropbox and iCloud the files may continue to take up space on the originating computer, and on any computer that has been "synced" to allow offline usage of the files.

For iCloud you control this behavior by the storage preferences:

Open "About This Mac" from the Apple () menu, then click Storage. There is an overview of your free space, space used by different types of files, and options for optimizing usage.