PicTapGo has a special group of Tools for making adjustments to individual areas of a photo. These Touch Tools all work in much the same way - essentially, you drag your finger across the photo to "paint" the effect into the area you want to change. Moving your finger back and forth over the same area will slowly build up the effect further.
Add / Remove
Every Touch Tool has a mode control (above the sliders) that changes how the effect applies. The modes are diametrically opposed, or in other words, painting an area in one mode will reduce the amount of the other mode in the same area. For instance, the Brightness touch tool has two modes: lighten and darken. More of one thing means less of another.
The size slider controls the size of the brush (how large the affected area will be with each move of your finger)
The feather slider affects the softness of the brush's edge (like the difference between a pen and a can of spray paint).
The Brightness, Contrast, Warmth, and Saturation tools borrow their algorithms from the Basic Adjustments tools of the same name. Intensity is the same algorithm as the Intensity Tool.