SCENARIO
The client requires to create a parent task and child task under the Project record.
SOLUTION
Go to project.
Navigatio: List>Relationship>Project

Select the required Project:
Under the Schedule subtab:
click on the New milestone:

Enter the name and other required details and save:

To create a child:
Click on the project activity button under the schedule tab of the project record
Enter the name
select the parent task
Enter the estimate time

Thus we have created a Parent and child record:
