I would have to get into a full tutorial on how to use it. not that it's hard but its just not easy to explain, but if you can understand Opacity, you can understand Flow. Well let me try. I sometimes use a low setting on flow - under 10% A LOT, and even down to 1%. Lets say you had it set to 10% and made a paint stroke. It would be similar to a 10% Opacity. Then if you made another 10% Flow on top of that, it would be like 20% opacity. Of course you don't have to do 10% and 10%. You can do 10% and then a 3%. This gives you MUCH MUCH MUCH better control on how a brush behaves. If you are brushing a mask, lets say you are masking someone's face in (and leaving the source image's hair), you would have higher flow in the middle and just a little bit of flow on the edges where you would be doing a lot more brushing to smooth it in. That's kinda the key to masking in the template's face when leaving the source image's hair.