I have recently had several people asking me exactly how to make seitan from scratch. It can be tricky as first. So, this is how I have learned to get the seitan to come out just right:
I use equal parts vital wheat gluten powder to water. Ex. 1 cup gluten + 1 cup water. Put the powder in a bowl and add the water right on top of it. The trick is to just massage the mixture with your finger tips and it will come together in a few seconds. You don't want to overwork or knead the dough, or else it will come out like rubber. There will probably even be a little water left in the bowl at the end. You want the dough the have the texture of a spongy brain, I know, but I can't think of any way else to describe it. It should barely stay together, but you should be able to form it into pieces that will become your "steaks" after they cook.
To cook them, fill a large pot with about 2 inches of water. I add tamari, chili powder, garlic cloves, herbs, vegan bouillon cubes, or whatever else I have around to add flavor while cooking, but put whatever flavors you like. Gently lay the pieces of dough in the water and bring it to a boil. Cover it with a lid and let it simmer on medium heat for one hour. Don't take off the lid! After an hour, shut off the heat, let them cool a little and remove them from the liquid. That's it! You can use it right away, put it in the fridge, or freeze it for later use. It's really easy and WAY cheaper if you are going to be using seitan in any significant amount. Also, don't get discouraged if it doesn't come out EXACTLY right on your first try, it might take a few times to really get the hang of it.
+You can also make it from scratch using a dough made from whole wheat flour and water, which you must knead under water until you release all of the starches by changing the water frequently to rinse them away. My experience is that this method is too time consuming and yields a lesser quality product than using vital wheat gluten. If you want to save time and frustration I would stay away from this method. Of course, if you're like me I'm sure you'll want to try it anyway.
Check out my basic seitan making video for some better guided assistance.