For example, I have 8 levels Over second off after quit the game.How to open second levels by default next time,I don't need to choose a level menu
You would use check points to save player data on their device this type of data includes the last checkpoint played Read the manual or search the forms for checkpoints there is a plethora of information on this
No. You use either checkpoints WITHIN one world or use different worlds. If you use different worlds like your set up above, then you can't use checkpoints. You need to set up a level select UI so the user can access them individually. If not, it always will start at the beginning. Checkpoints are only used within the same world over several scenes. So you need to convert your worlds into scenes within the same world.
try this, do that way like this, with each world you like, but do not forget to put "event observer" in the menu to all the worlds and do not forget to put and "points" in all worlds at the end to determine the where to start when returns