Let's see, This will be from memory but I used to have one of those. Take your blade material, cut the appropriate length, put on a pair of gloves, this part can get you cut up a bit. Take the blade material and hold the two ends together with one flipped so the teeth face opposite of the other (kind of puts the blade into a big tear drop shape, with you holding the point), take the edges of the blade up to a disk sander or grinder and grind them both smooth, you don't have to be exactly perpendicular, that's why you flip the blade material, so if you are slightly crokked it'll match when you but the two edges together.
Put the blade material into the welder all the way back into the jaws and butt the two pieces together in the center of the area between the jaws, lock the jaws tight, set the heat lever to the correct width of saw blade you are making. Push down the big lever (mine was red), and hold it there as it fuse welds the blade, then let up and let the blade cool for 20 seconds or so before you unclamp it.
The blade will be pretty brittle at this point so be careful, take it to a pedestal grinder and carefully flex the blade just a bit and grind the excess material from both sides and even up the back of the blade. Now you've got nice shiny spots on the welded area of the blade, put it back in the welder, not all the way in this time, leave the teeth sticking out of the clamps, and push in on the "anneal" button, I would ususally not do a constant hold in on it, but more of a push, release, push, release, until you bring the bright spot past straw and just barely to a blue color, let it cool for 20 seconds or so and you are ready to rip and tear. I hope that helps and I didn't forget anything, it's been a few years since I've done it.
Brian