[TommyW]

I found it pretty straightforward really.

There seems to be two ways you can work this and they can be combined.

I do the first one: Use the sidebar

The folders in the sidebar can function as Uber-projects, with regular projects functioning as effective sub-projects in them.

You can also nest folders and have further structure. Be as elaborate as you want.

The other method is...

In the main window, you can indent tasks or make child as other posters point out. When that happens, you have to manage it a little, it's more like a straightforward outline, there isn't necessarily a sense of 'projecthood' if you get me. The parent line is made bold to indicate difference, that's good. While you can create any amount of nesting, a true outline, when you check off all the tasks in one subproject, it isn't automatically checked off. So you have to mind it a little.

But between the two ways of working you should be able to do pretty well anything.

But I think that in terms of GTD... and I know that OF wants to be more than just a GTD app... it is good to try to keep it to as simple a structure as possible. I try to keep it to a one level of nesting and the sidebar is definitely the most clean way of doing that.