Finally, in the call flow tab you direct how the number will direct through to the ring group. Will it call the number directly of pass through a time condition, an announcement or an Auto Attendant (IVR). 
With each stage of a call there are a limited series of actions that can occur. These are listed once you click the edit button on the call flow. If the call flow has not been set up it will automatically enter edit mode. By clicking on your chosen function, and dragging it onto the screen in the appropriate space you create a new instance of that function.
You then need to create a link between the function and the call by choosing the plus button, resting the cursor over the S button and dragging it to the next function.
See tutorial on the screen.
In the example below. The number routes through to a time condition. If it is during working hours the call rings an auto attendant. By pressing button 0 the call goes to the main ring group, by pressing button 1 the call goes to the fail-over group. The calls then fail over to a common voicemail. If the call is outside of working hours (as defined by the time condition) it goes straight to voicemail. 