I'd suggest just trying a couple rooms to get the feel of it. Take the backgrounds that you have, no matter what size they are, and make a room for each. Then fill each one with walkable area so you can walk around them. Then use the debug command ctrl-x (unless you've changed this) to warp between those rooms. You can also try creating different projects with different screen resolutions and doing the same thing. It only takes a few minutes and it's definitely going to help you understand it more than us explaining it.