You take your level integer, use that to populate the scene, and probably show some UI text that this is level X. After the player completed it, you add +1 to level, perhaps do some cleanup (pool/destroy objects, reset things), rinse and repeat.
If objects have some starting position, initialisation, and can be moved around etc. you can make a RESET (example name) global event, which you might add to the START state. At the end of one level, broadcast RESET and everything is set to the start state.