Tutorial 3: Create and assign contexts
It’s handy (or, for some people, crucial) to assign a context to each action. A simple way to think of contexts is as the place or mode you need to be in to do a given task: you can only make phone calls when you’re near a phone, you can only buy groceries when you’re out running errands, and you can only do research on the web when you’re at your Mac. These are contexts, and if you think about it, almost any task requires you to be in a certain context to do it.
Switch to context mode by clicking the @ sign on the mode switcher: 
While the planning mode's blue sidebar holds your projects, the context mode's purple sidebar holds your contexts.
OmniFocus comes with a few contexts already created for you. Add some new contexts by clicking the plus button below the sidebar, or double-click an existing context's name to change it. Make as many contexts as you need for the various places and modes you have for doing work: Home, Office, Mac, Errands, Phone, and so on. You can always add more contexts later on when you find that you need them.
Now, go back to planning mode by clicking the little project icon on the mode switcher: 
Open the pop-up menu on each action (where it says No Context), and choose from the contexts you just saw in context mode to assign a context to each action.
