Step 3: mix it up, add water
Put all your ingredients in a glass or ceramic container like a jar or bowl. You don't want to use plastic because the increasing amount of acid can react with it. I'm not sure about what metals are reactive, so I'm avoiding metal containers, too.
Stir it up.
Add water - Use non-chlorinated water, because it will kill the bacteria that we are trying to promote. I used tap water that I set out in a bowl for a day to let the chlorine evaporate out. Maybe you have some better water.
Pour water over the dry ingredients until it just covers the surface. In a few hours the oats, nuts, and seeds will absorb some of the water and expand, so the water will not cover the surface anymore. We want a consistency of a thick oatmeal (it basically is just thick oatmeal).
Cover the container with a cloth to keep dust and flies out.
Optional - You could add a spoonful or two of active yogurt or soy yogurt to the mix. This would introduce those specific bacteria strains. I think it's unnecessary because the bacteria naturally present on the food and in the environment will do the job, and they are much more diverse.