Once you've established metadata fields, you can generate subcategories to further refine your data by following these steps.
Create Custom Metadata Subcategories
Go to the Assets tab.
Scroll until you see Custom Metadata.
Find the Category you want to modify.
Hover and click the plus sign icon when it appears.
Give your new subcategory a name.
Click OK.
Tip: If you want your users to enter new information instead of choosing from preset categories, use the Open Text option.