Talk to any prospector who uses the Le Trap Square Pan and they'll swear up and down about how it's the best thing since sliced bread, while a few others will mill around muttering under their breath about how they never could get the hang of it, while those of us who've never tried one just stand there looking at the rest like they've just seen an alien.
Truth is, they're an odd looking gold pan, but they really do work. The secret is in the riffles that offer more gold catching surface than traditional pans. They're set at just the right angle to catch gold as the lighter material is washed out of the pan with a bit of a forwards and backwards rocking motion.
At about 18" long x 12" wide x 4" deep, there's room to process quite a bit of material...fast.
If you've landed on this page, my guess is you know somebody who swears by the Le Trap and they talked you into buying one. That's great! Hopefully they can give you a detailed "how to pan for gold with a square pan" lesson, but I'll give the basics a fair shot.
Essentially you load it up about 2/3 full with material, fill with water and slurry as normal. then you fill and pour, fill and slurry and pour, fill and slurry and pour - back and forth. The front wall of the pan acts a bit like a mini sluice box trapping the gold and heavies. Get it down to a couple tablespoons of material, then move the material to the front edge of the pan and wash the black sands backwards down into the square bottom. The gold should stay up on your riffles (though some may end in the bottom of your pan).
Best of luck with your panning! I hope it works for you and you join the "best thing since sliced bread" camp!