Click into Keyframe 1 of the layer background.
Import the soldier.jpg image to the stage. It
should fit nicely in the middle of the 550 x 400 default stage size.
If you need to change the stage size, click on an empty bit and
alter its size in the properties pane.
Nudge or drag the image across to the left of the stage.
Then click on the lock/unlock option in the background
A closed padlock icon will appear in the layer's information area
and the image will then stay where you put it unless you unlock
the layer. You cannot accidentally alter it.
Locking layers does not alter their appearance in the movie but
it does save you a lot of time rescuing objects that have been deleted
The show/hide option beside it is also worth experimenting with
when the stage gets a bit cluttered.