Are SharePoint columns part of metadata? Is this because columns make it easier to find information within SharePoint?
So, Metadata is actually added information that will help you categorize and later on find the information you are looking for.
Think of your MP3 collection (Or streaming service), your documents are the songs, then you add it's artist, genre, album, year, label, so on and so forth. So you want to find Rock music, you search by Rock, you want to find everything released by X label, you can do that.
Now think of the columns as how you populate your song information.
Metadata at it's most used form.