Assigning content to categories is a simple process through the content tab.
When you are creating or editing content, you will see the ‘categories’ field.
Assigning the category here will allocate the content to that category or sub-category. If you do not assign a category, the content will be displayed in the MISC folder in the library.
You can edit the category, which will re-assign the content piece to that new category.
Note: Content visibility is determined by content groups, not by the category. Read more on the content groups to determine how to allocate visibility to the content.