Power Brush is a filter that can be applied to the contours of selected elements. When you select Element > Make Power Brush this creates a “live” brush stroke along all contours of the current element (or selected elements).
You can use the Brush panel or the Property bar of the Glyph Window to change the brush parameters, and they will be applied to the element that uses the Power Brush. You can leave the element with the Power Brush applied, or at any time, you can convert it to final outlines via Element > Expand Filters command or by clicking “Expand” in the Brush panel or the Property bar.
To remove the Power Brush filter, from the particular element, select it and click Remove in the Brush panel or the Property bar.
See also the Brush tool section to learn how to draw with Power Brush.