The step by step process is described in the following url.
Key information are as follow:
In particular, for the Google Gantt chart tool to work correctly, you should include columns with the following data.
Unique ID (optional) – This column will contain a unique number assigned to each row of the table (1, 2, 3, 4, … for example). You only really need to include this column if certain tasks in your list are dependent on the completion of other tasks and you want this information reflected in your Gantt chart. If not, you don’t have to worry about this column.
Name – In this column, include the name or a brief description of each task.
Start – Enter the proposed start date for the task in this column.
Finish – This column should contain the proposed or actual completion date of the task.
Percent Complete – The number in this column should indicate what percentage of the task has been completed. Tip: Leave off the percent sign in order for the Gantt chart tool to read this field properly.
Prerequisites (optional) – Like the Unique ID field, this column is only needed if certain tasks are dependent on others. If they are, input the Unique ID of any prerequisite task here.
Note that you can give these columns any title you wish and that you can include additional columns with other project data – just make sure that the above information is included somewhere in the table.