Draw a Path with the Brush Tool
Brush is a freehand drawing tool. It creates a path that follows the cursor as you draw. The Brush tool is, in fact, the Draw tool that draws with a Brush stroke.
To activate the Brush tool, click on the Draw icon in the Tools panel. Before using it, make sure that a Brush is selected in the Appearance panel.
Settings of the Brush tool are located in the Control panel. They are described in the Create a Path with the Draw Tool section.
Brush does not use the pressure information when you draw with a stylus. For that reason, the state of the Pressure check box carries no effect while using the Brush tool.
Once you finish drawing, you can modify the created graphic. To edit the path, use tools and methods described in the Edit a Path section. To change how your graphic element looks, use the Appearance panel.