In some cases, you may need to link two content folders instead of using a drop-down selection. For example, the blog category.
It's better to create a content type and folder called 'Category
Create a text field and add some categories.
To link two content folders, click Contents - Contents on the main navigation menu. Click the 'Setting' button
In the popup window, switch to the relation folders tab, click '+' button to add a folder.
Select the folder you want, set the alias and click 'Save'.
Now when you add a new blog article, there will be a field to let you pick the category.