GanttView allows you to add special instructions while adding a task to your project. Notes can be helpful in providing further information for each task. You can add notes for each task using the Notes property of the Task class.
To make the task notes appear in the grid column at run time, click the Grid Columns button in the toolbar and select Notes from the Grid Columns dialog box.

Use the below code to add notes for your task programmatically.

//Add notes for a task
Task1.Notes= "This is an important task";