How To Implement Tap To Start Screen With Background Preview Of The World User Has To Play

I have a game similar to ball flipper template and i'm unable to achieve the following

1. Each world of mine is of different mechanics and nothing to do with levels inside, after I clear levels in world 1 i move on to world 2. But when I close my app and open it, it always starts from world 1 ( please note that i'm only using single scene world and no distance based checkpoints

2. How to implement Tap To Start screen, I want the background to be shown of the world . If user is in world 2 then when re-opened, tap to start to be shown where behind is the world 2. and on click of Tap to start, it continues with the world user has to play