How do I add ordinals to my font?

I’m trying to figure out how to add ordinals like the feminine a ordinal and the masculine o ordinal to my font. Can someone break it down for a dummy like me?

You can right click on the “Mac Roman” entry in the sidebar in font view. You should get a popup with all missing glyphs and you can pick the ones you need.

Or add new glyph with the plus button in the lower left of he Font View and then rename the glyphs to ordmasculine and ordfeminine.

If you know how to type it or copy & paste from somewhere, you can go to Glyph > Add Glyphs and type the character there (you need to space each glyph, otherwise Glyphs thinks you want everything as one ligature glyph)