It’s really pretty easy. On brew day, I scavenge enough spent grain (before composting the rest) to fill a couple baking pans about a quarter inch deep. The baking pans go in the oven at ~175F while I boil wort. I check on the grains, stirring and breaking clumps as needed until the grains are dry. It usually takes several hours. When the grains are dry, I bag them in a ziplock, then use as needed. To grind them into flour, I use an old Bosch 2-blade coffee grinder, which also get used for grinding spices. I just sub a small portion of sbg flour for some of what the recipe calls for. Over time, I have increased the portion of sbg flour.
Sometimes, I bag the wet grains and freeze them. When I need some sbg, I thaw, then dry as above. I love what the sbg flour adds to my baked goods. They make a good addition (in small quantity) to pancakes. I want to try some in pizza dough, too.