Tutorial 9: Overachievers' Corner
If you're ambitious, try getting your diagram to look like this. 
It might be helpful to lock the background layer by clicking its little padlock icon in the utility drawer; this prevents you from accidentally selecting or changing the background image.
The title can be created with the Text tool, the style of the connection lines can be changed from the Lines and Shapes inspector, and the positioning of the line labels can be changed with the Geometry inspector.