Files & folders share the same set of tags. While clips in the Clipboard tab have their own set of tags.
To add a new tag go to the Tags pane in Filezo and click on the + button from the top toolbar.
To edit an existing tag (name, color etc), go to the Tags pane, right click on the tag you wish to edit and choose 'Edit' from the menu.
To delete an existing tag, go to the Tags pane, right click on the tag you wish to delete and choose 'Delete' from the menu.