Hello there Steta,
The process is fairly simple. The tool you need to use is Draw > Insert File. You will be able to place and size it. However, since you need to draw on top of it, make sure you crate a new layer and sheet that will float just above the background; and place it on these entities.
There should be a more detailed entry in your CC3 help file along the lines of 'Adding a background image'. I apologize I am not on the correct computer to verify the name.