You can use this scrolling super world to make your world infinite. This super world contains a world superclass and a actor superclass for creating a infinite scrolling system. You just have to add your scrollingActor to the world and he'll be able to move in the scrolling world. You also can make the world a fixed size (also only the height) if you don't want it to be infinite. If you download it you'll find examples and explenations in it that tell you how to use it.

It would really depend on what you wanted to do with your scenario. Is it an infinite side-scroller? or a finite side-scroller?.... Will the main character be able to scroll back the other direction? or only be able to scroll one way? .... Will you have a scrolling world background? or not? .... Will all actors in the world be scrolling? or are there some control objects (score-/level-/life-counters, health-bars and the such) in the world? All these will have to be considered to determine which scrolling class would be appropriate (whether one is downloaded from the site or self-created).