I think you do understand the gates, I think you were just having some trouble with the output count of the recipe.
So the fuel pellet recipe outputs 2 and not 1, that means that the gate will be open long enough for 2 items of porcelain to go through at that belt speed. You can fix this by making the output belt twice as fast, or by making a splitter setup at the output belt, so that the gate detects half the number of items.
I would also advise you to make the output belt longer, so that you don't get weird timings and stuff. If the funnel is trying to place items where the gate is detecting, it could result in the belt only detecting "half" the item, meaning that it doesn't detect the item's full passage, and it could result in the gate staying open less than it should.
