Rosie, I’m not sure of what you’re asking but from what I gather I think you’re asking about the brush size and the “fuzzy” soft edge of the brush. The size of the brush and the softness can be controlled independently in several ways.  First, (while brush tool is selected) by using the brush palette. Once the brush palette is opened select “brush presets” there you will find “Master Diameter”. This controls the brush size in pixels. Then select “brush tip shape” there you can select “hardness”. This slider controls the brush softness in percentages.

 

Secondly, once the brush tool is selected…up at the top menu bar you’ll see the brush size with a dot and a number underneath it. Clicking on this will drop a window down with both sliders: brush diameter size and brush hardness.

 

Thirdly, the brush size can be controlled using the keyboard shortcut keys while the brush tool is selected. The bracket keys “ [ ] “will control the brush size. Also, holding down the shift key and tapping the bracket keys will control the “hardness” and it can be seen while watching the brush circle in the menu bar as it will change the edge appearance. I hope this helps.