This is an Adventure game. As such, the game play follows a number of adventure game genre tropes. Typically, a level will begin with the protagonist being met by somebody who gives them their task. This task might require them to gather a number of items, to gather pieces of information from written sources and/or other people, to explore and interact with the environment, and to solve puzzles. Some tasks might require a combination of these actions.
That was an apocalypse, adults got sick and died. there are a few of children survival in a valley and now they must travel over the world, looking for other survivors and places to live.