Here it goes:
First you have to hammer nails all around your window, against each piece of glass, to hold the whole thing in place while you solder. You don't want it shifting.
Next you apply the flux. Yes flux, as in the flux capacitor. As in space travel, Michael J Fox, disrupting the space-time-contiuum, etc. Only this is just a clear gel that helps the solder to stick. Not quite as cool. But way safer.
You start by fluxing and soldering just the joints--wherever two or three pieces of glass meet at an angle. You hold the spool of solder right next to the joint, then you press the soldering iron up against it and quick as a wink it melts into a shiny puddle of metal that fuses the joint together. It's really fun to do.
Every so often, you clean the gunk off your soldering iron by rubbing it against this sort of white stone. It smells delicious. Kind of a cross between burning hair and steaming hot garbage bins.
Next you flux all the rest of your copper foil edges and solder them. Then you flip the whole window over and repeat. You'll probably go back over most of the joints and some of the straight edges to smooth down the solder. This is where experience comes into play (which I have none of): because you don't want those joints to be lumpy. You want them smooth and fluid. This requires reapplying solder, removing solder where it's too thick, and smoothing it down with the hot solder iron to get rid of bumps. One of my favorite parts of this step was shaking excess solder off my soldering iron onto the floor. You'd sort of collect it on your soldering iron, aim your soldering iron down, and shake it. As the droplets would hit the floor, they'd instantly cool, making this awesome metalic dripping sound. It sounded like "Pthp!"
The next step I didn't photograph for whatever reason, but this is where you add the lead edging. It makes the frame around the whole window, keeping it together. It has to be soldered to the existing solder, but the lead edging is much thicker and melts slower, so you have to hold the soldering iron in each spot longer.
After the entire window has been soldered and you've spent agonizing hours smoothing and resmoothing it and then given up and accepted that it'll never be perfect, you clean it and remove all markings. Now you can add petina. Petina choices are copper, silver, or black. I went with copper. So you rub all the metal with the petina and it changes colors! (You can see below how it is copper below/right and still silvery to the left of my hand.)
Finally, you want to be able to hang your window up, so you solder in some nice rings to wrap the wire around.
And you're done!