Hi Michael,

From my understanding you want to create a parent/summary task and several subtasks to go underneath it. Here's how to do that in gantter.

1) Select the task's underneath the soon to be summary task you want to it's subtasks. Then go to the indent to the right arrow on your horizontal toolbar.

2) Once clicked you will see the parent task is now marked as bold and as a black bar in the gatt chart view and that any dates, cost, durations, etc... will automatically calculate up into the new summary task. 

Hope this helps, let me know if you need anything else 

Kind Regards, Sophia