A food processor will not achieve a fine enough grind.
Grind the seeds until they're fine, like a flaky powder.
When the meal begins to clump together, that is generally fine enough.
It is best to grind just the amount of flax seed meal or chia seed powder you need, at the time you need it, because exposure to light and oxygen will compromise the nutritional benefits.
The next best option is to grind a few days' worth or a week's worth and store it in the freezer in a dark colored jar, to minimize light exposure.
Mix with water
For every egg in the original recipe, use 1 tablespoon flax seed meal or chia seed powder and 3 tablespoons water.
Whisk together in a separate bowl, and let the mixture sit for about 5 minutes.
It will get gummy, just like eggs.
Add to recipe in place of eggs
Then the mixture can be added into the recipe where it calls for egg(s). No other adjustments are usually needed!
Usually, you will not be able to tell any difference in baked goods where flax seed meal has been substituted for the eggs.
However, small items like cookies may be more crumbly. I recommend making cookies as bars. Anything that bakes as a bigger solid -- such as muffins, quick breads, cakes, or bar cookies -- will do just fine.
If you use too much flax seed meal/water mixture (or if you use any flax seed meal/water mixture in pancakes), the risk is that what is baking will remain gummy inside.
That's why I don't use any egg substitute at all for pancakes or pancake-style flatbreads.
They just don't cook inside before getting burned on the outside.
How To Use Flax or Chia as Egg Substitutes https://traditionalcookingschool.com/food-preparation/weekly-kitchen-tips/great-egg-substitute-flax-seed-meal/