I've tried various settings, and get different results, but I don't understand how flow percentage affects the outcome. It seems to affect how "fast" I get to the maximum opacity set for the brush in an uninterrupted stroke, yet if I set it to, say, 25% with opacity of 50%, even the first movement of the brush gives me a much thicker layer of colour than 25% of the 50%. Looks more like 75 or 80. And it also seems to depend on brush spacing.
Can someone explain in a simple way what flow is and how it works together with opacity, please?