Step 2: How to mount the glass to the frame.
Professional made windows use a special routing (or shaper) bits to create a tongue and groove assembly but that is expensive to buy and time consuming.
I could just build the frame and surface mount the glass using mirror holders (an L shaped piece of plastic that screws into the wood and holds the mirror in place with a tongue that extends over the glass). I Really do not like this one as the edge of the glass is exposed and the frame would be wobbly as the glass is not part of the structure.
Finally, the method I used is simply to rout a 1/4 inch slot into the wood and put the glass in. I used "Space balls" ( I swear that is their name). They are 1/4 inch rubber balls that go into the slot and keep the glass from moving and protects it from shock. rubber washers cut up and inserted into the wood would work just as well.