Draw Tool
The Draw tool allows you to draw free-hand strokes.
In the Tool Settings select the brush and material to use with the tool.The Draw tool uses Draw Brush types.See for more information.
Common Brush Options
Click and hold LMB or use the pen tip to make free-hand drawing on the viewport.
Stabilizer
Shift-LMB toggle the use of Stabilizeron the brush to have more control while drawing and obtain smoother lines.
Switching to the Erase Tool
Ctrl-LMB changes temporally to the active erase tool.see for more information.
You can also use B to delete all the points in the selected drawing area.