you can save the levels as a string for example, and read them out, when the next level should appear. example: " 000000000000000000000000000000000000 000000000000000000000000000000000000 000000000000000000000000000000000000 000000000000000000000000000000000000 000000000000000000000000000000000000 000000000000000000000000000000000000 000000000000000000000000000000000000 000000020000003000000003000000300000 111111000111111111111111111111111111 " For this example every "0" means theres nothing, every "1" menas there´s normal ground, "2" menas there´s a moving platform, every "3" means there´s an enemy.

For any new level, you can create a method in your world that removes all objects, then adds new background, new objects, etc. I would just keep any data about your game in a variable held by the world. You may even keep the score and data in some type of scorekeeper object, but be careful to remove everything but that one, or save it on the side while you wipe everything else out.

Blight, if you need more help, you should post some code to show what you have and what you're having trouble with. The question is way too general otherwise.