It is also useful to note that there exists a bitmap system which is covered in the help files, and often there is a camera system in action when you run a DBP program.
There is a bitmap under the ID of zero which represents your screen; which also receives 3D rendering from a camera, the default camera being number zero; if there is anything to render.
So as far as DBPRO is concerned; bitmap zero is the screen; so if you use the command; Load Bitmap "File.png", 0, this will load the image on screen
Load Bitmap "C:\File.png", 0
wait key
If you run TheComet's example, DBP pastes a seperate image onto bitmap zero much like what happens in photo editing. Bitmap zero which is also by default the -Current Bitmap()- and also the screen is what TheComet is pasting on. His reference to the Sync command is like a refresh call; only necessary if auto refreshing is switched off by calling -Sync On-. If you used -Set Current Bitmap- to change to a different bitmap loaded or created with -Create Bitmap-, his operation would paste the image there, but not on the screen.
It is also useful to note later on in your activities, that images are often used for 3D rendering.
Indeed there is a lot happening; and alot is covered in the help files and various forum threads. You can even texture or apply special shaders to cameras, another way to fill the screen.