Draw paths and apply brush strokes simultaneously

Select a brush in a brush library or the Brushes panel.
Select the Paintbrush tool .
Position the pointer where you want the brush stroke to begin, and drag to draw a path. A dotted line follows the pointer as you drag.
Do one of the following:
- To draw an open path, release the mouse button when the path is the desired shape.
- To draw a closed shape, hold down Alt (Windows) or Option (Mac OS) as you drag. The Paintbrush tool displays a small loop . Release the mouse button (but not the Alt or Option key) when you are ready to close the shape.
  
  Illustrator sets down anchor points as you draw. The number of anchor points is determined by the length and complexity of the path and by the Paintbrush tolerance settings.
  
  To adjust the shape of a brushed path after you finish drawing it, first select the path. Then position the Paintbrush tool on the path, and drag until the path is the desired shape. You can use the technique to extend a brushed path as well as change the shape of the path between the existing end points.