[Ken Case]

It works exactly like OmniOutliner: drag a little to the right, and it indents and becomes a child task. Drag underneath, and it becomes a peer. Drag to the left, and it becomes a parent (which means that it can become its own separate project, if you drag it to become a peer of the project itself).

Task groups can be either parallel or sequential, but the UI is currently missing on task groups themselves. (Right now you can set that state by temporarily making one a project, or by using AppleScript, but before long you'll be able to do it directly on the task group just as you can on projects themselves.)