There are two ways to add a story to a group: from the "+groups" button on the story's page, or from the "add story" button in the group's folder.
But if that group's folder has 0 stories in it, the "add story" button does not appear in the group's folder. As long as that folder has 0 stories, you can only add a story by the first method with the "+groups" button on the story's page.
Once a story has been added with the "+groups" method, the "add story" button will appear in the group's folder, along with the listing of the stories in the group.
There are two ways to add a story to a group: from the "+groups" button on the story's page, or from the "add story" button in the group's folder.
But if that group's folder has 0 stories in it, the "add story" button does not appear in the group's folder. As long as that folder has 0 stories, you can only add a story by the first method with the "+groups" button on the story's page.
Once a story has been added with the "+groups" method, the "add story" button will appear in the group's folder, along with the listing of the stories in the group.