Manage The Levels in unity : Beginning To Ending

Hello, I am working on a game in which I want to get my player do multiple tasks in a single scene/environment. I want to control these different tasks or levels with xml file. But problem is how to begin and end the level in same scene again and again and how to store the data again when finished. When the game ends, I want all the updated score to be added to last level crossed so that next time person can resume from there.

Can any one suggest the possible way of how to do this. It would be great help

Thanks in advance :)