I want to add a border to my photos in a book I have created in Mac Photos. However, when i select " edit photo" , there is no option to add a border/ frame. The only option are "filters" and "zoom and crop". Help. How do I add a border?

Use a book theme that puts borders around the photos, for example the Journal theme. And use a colored background.

There is no editing command to create borders. You would have to export the photo and add the border in an external editor, Photoshop Elements, Pixelmator, FX Studio Pro.

For example, some of the frames in FX Photo Studio Pro:

You are referring to this help page? https://help.apple.com/photos/mac/1.0/?lang=en#/pht337d0a03

1. Click a filter or a border to apply it to the photo.
2. 

I have never seen the "border" part appear in Photos for Mac. It must be a left-over from iPhoto iOS.