To make the mirror frame, Kevin first used his table saw to cut a 1/4 by 1/4 groove in the corner of the 1-inch square trim piece. This would create the little notches where the trim would rest on the edge of the mirror.
With the grooves in place at the edges of the mirror, he used 2-inch nails to secure the frame around the mirror where needed.
You can get some wood hole filler in the wood color to fill in those nail holes.
You could also stain or just seal the wood. But I’m not sure what I want to do with ours. I just love the look of raw walnut wood! A sealer would make it more rich and shiny.