This is mostly how I take crabs.....
It is farely simple, once you get the hang of it. What I do is, pull off the claws and save them if they're large enough. Then on the bottom side I pull off the abdomen then by gripping the largest marginal spine, I pull apart the top shell from the bottom shell. Remove guts and gills, then you can procede to use a knife or small spoon to remove the meat from all of the separating sinuses or open spaces. Takes quite a few crabs to make up good amount of meat. Then get you a good recipe for crab meat and make some stuffed flattie or crab cakes or whatever you prefer.
I'm sitting on about 3/4 lb of crab meat, without a flattie to stuff them with............Need to go fishin I guess... Good luck!!