When reading about subtask on  https://www.zoho.com/projects/sub-task.html I see the term "Summary Task" mentioned. What is this and where do I find it in Zoho Projects?

This page also talks about a double-arrow button used for indenting or outdenting tasks to create subtasks. This button should be visible by hovering the mouse over a task. I am also unable to find this feature. 

I am using the Enterprise version of Zoho Projects.

Best Regards

Johan