Adding stuff to the Inbox
The inbox is a kind of intermediary area between your brain and your OmniFocus library. Whenever you have something important that you don’t want cluttering up your mind, but you’re not quite ready to meticulously file it away in the right place in your OmniFocus structure, just put it in the inbox. Later on, when you process the inbox, you can decide whether each item is a new project or an action in an existing project, what its context is, and so on.
To create a new inbox item, just select the inbox (in the sidebar or in the main outline; a quick way is with the Inbox toolbar button) and press Return. Type whatever’s on your mind, forget about it for now, and get back to whatever you were doing! For extra bonus productivity-streamlining finesse, don’t even switch to OmniFocus to do this; use the quick entry window or the clipping service instead.
You can create hierarchy in the inbox by using the Edit ▸ Outlining menu commands, if you already know that something is going to have sub-items. Later, you can add these groups to an existing project or make them into full-fledged projects themselves.